High efficiency, high output, compact CD ignition coil

ABSTRACT

A high efficiency, high output, compact ignition coil particularly suited for use in capacitive discharge, multiple pulsing ignition systems, with about ten turns of primary (1) wire (Np) and about five hundred fifty turns of secondary (2) wire (Ns) for an input voltage Vp of approximately 350 volts and a peak output voltage Vs of 30 kV, the core and windings of the coil featuring separate and different primary (31) and secondary (41) core halves structured on the basis of herein developed coil open and closed circuit criteria such that the core half (31) containing the primary winding has a large center post (32) of cross-sectional area Ap with a narrow slot of width W1 around the post (32) for winding the primary wire (1) to provide essentially the total required coil leakage inductance Lpe of about 50 uH for an input capacitance of about 5 uF and spark discharge frequency fcc of about 10 kHz, and the secondary core (41) structured to have a center post (42) of cross-sectional area As about half that of Ap to provide a much larger winding width W2 than W1 to efficiently support the many layered larger coil secondary winding (2) for a same overall outer core diameter D of the coil comprising a pot core or &#34;E&#34; type core structure.

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to ignition coils for ignition systems forigniting air-fuel mixtures, and particularly for use in systems usingcapacitors for storing higher levels of ignition energy, i.e. highenergy capacitive discharge ignition systems, and for delivering theenergy in the form of a rapidly pulsing (multi-strike) sequence of sparkpulses.

Considerable research has been conducted on ignition systems forinternal combustion engines for improving their capability to igniteair-fuel mixtures. More specifically, during the past few decades, therehas been work done on improving the ability of ignition systems toignite air-fuel mixtures with poor ignition characteristics, especiallyof the inherently cleaner and more efficiently burning leans air-fuelmixtures.

Much of the prior art work on so called high energy ignition hasfocussed on alternative approaches other than coil design for deliveringhigh ignition energy. Little attention has been given to improving theactual coil design, particularly in view of the recent development ofthe high efficiency, voltage doubling, low turns ratio coil principledisclosed in U.S. Pat. No. 4,677,960 referred to hereinafter as theVoltage Doubling Coil principle, or Doubling principle for short.

Prior art work on spark ignition, including ignition coils, arenumerous, and for example, are summarized in Edward F. Obert's book,"Internal Combustion Engines and Air Pollution", pp. 532 to 566,Spark-Ignition Engines, Intext Educational Publishers, 1973. The workreported by Obert, and the work published since then, including the coildesign presented in the above patent, are based on well establishedprinciples of designing coils by either winding the primary andsecondary windings essentially concentrically, or on different arms of aclosed magnetic core for high leakage inductance. Included are variousways of performing the winding, especially the much longer secondarywinding, and these are well known to one skilled in the art.

SUMMARY OF THE INVENTION

On the other hand, the present invention is based in part in a)recognizing that the open circuit (high voltage) and the closed circuit(high current) properties of ignition coils can be separated, especiallyfor approaches based on the Doubling principle, and that each part ofthe coil is different and can be designed to be optimized separatelyfrom the perspective of minimizing resistive and core losses and coresize and overall coil size, and b) acting effectively on the basis ofsuch recognition.

Specifically, the effective constructions of two different corecross-sectional areas and core shapes are arrived at for the primary andsecondary windings, the secondary requiring about half or less the corearea of the primary depending in part on the output capacitance and corematerial to accomodate a larger winding area. Moreover, given that ahigh leakage inductance Lpe is preferred, i.e. of about 50 microhenriesfor an input capacitance Cp of about 5 microfarads, a preferredembodiment is developed in which the windings are placed axiallyside-by-side for easy containment in each half of pot or E type core,having low EMI, i.e. electromagnetic interference. As a further result,for a primary voltage Vp of 350 volts, a preferred design is possiblewith only about ten turns of primary winding (and 500 turns of secondarywinding as per the Voltage Doubling principle).

As part of an overall optimized ignition system as disclosed in U.S.patent application Ser. No. 131,948, the present coil structure family(i.e. family of designs of such structures within the present invention)lends itself to a more optimally defined spark pulsing wave shape of thecapacitive discharge circuit disclosed in that patent application,including the recharge circuit disclosed therein. Moreover, such newcoil structures make possible further system optimization andextensions, as in distributorless ignition systems now made possible bythe compact nature of the coil structures. For example, for suchdistributorless ignition system applications, there is disclosed animproved spark plug wire based on principles disclosed in U.S. Pat. No.4,744,914, which tunes the capacitance spark generated by the coilinvention to allow the spark to pass with minimum attenuation whilestrongly damping the high frequency spark components (greater than 30MHz) which cause EMI. And furthermore, when used with the preferredspark plug of the Electric Field Focussing Lens (EFFL) type disclosed inapplication Ser. No. 131,948, the coil is preferably designed to give apositive versus conventional negative initial high voltage outputpolarity.

In another aspect of the side-by-side winding feature of the coilinvention two different magnetic materials can be used for each corehalf, a low loss (preferably ferrite) material for the half in which theprimary wire is wound and a low cost (higher loss) high magneticsaturation material (preferably Silicon Iron) for the half on which thesecondary winding is wound. Furthermore, the high leakage inductance(Lpe) primary winding of the coil can be divided into two parts, a firstpart (Lpe1) that is coupled to the secondary winding through eitherconcentric or side-by-side, i.e. colinear windings constituting atransformer (the coil), and a second part (Lpe2) that is contained in aseparate stand alone core comprising a separate leakage inductancechoke. This design provides several important advantages.

One advantage is that by decoupling part of the primary leakage windingfrom the secondary winding it reduces the AC losses of the secondarywinding due to a lower primary winding leakage flux cutting thesecondary winding turns. It also reduces the overall transformer corelosses by weighing the total core losses in proportion to the leakageinductance of each part so that the lower loss separate leakage choke(the second part) can have a much higher weighting factor (by designingLpe2 to be much greater than Lpe1). In this way lower cost, highermagnetic saturation, higher loss material, e.g. Silicon Iron (SiFe), canbe used for the first transformer part to reduce overall cost.

A second advantage is that the separate leakage choke permits especiallysimple and low cost forms of distributorless ignition by allowing thesingle leakage choke Lpe2 to be shared between several transformer coils(of very low leakages Lpe1i) which can be made very small and cheapthrough the use of SiFe laminated magnetic core material.

CERTAIN FEATURES AND OBJECTS OF THE INVENTION

The following stated features of the invention are part of thedescription of the invention itself.

It is a principal feature of the present invention to provide a new andimproved ignition coil which is compact and efficient (low number ofwinding turns and hence low winding resistance) and is suitable for usein very high power (hundreds of watts), high efficiency, multi-pulsingcapacitive discharge (MPCD) circuits based on the Doubling principle,for igniting very lean and otherwise difficult to ignite air-fuelmixtures. In particular, it is a feature to provide new coil designcriteria for separately located primary and secondary coil windingsbased on the closed circuit and open circuit operation of the coil whichdefine the design of the coil structure and windings, such that the coresizes of the two separate windings based on the new design criteria leadto secondary winding core cross-sectional area about one half of that ofthe primary core cross-sectional area.

Another feature of the present invention is to design the core halvessuch that under normal operating conditions the respective core halves,for low loss core ferrite material, are stressed to near their magneticflux-density saturation levels.

Another feature of the present invention is to advantageously use thenew coil design criteria to develop coils suitable for MPCD applicationswith only about ten turns of primary wire for about 350 volts of coilprimary side voltage Vp with each winding preferably contained in eachhalf of a pot or E type core.

Another feature of the present invention is to design the coil to beused effectively with an MPCD ignition circuit including preferably arecharge circuit (an MPCDRC ignition) to provide closely spaced, e.g.250 to 500 microsecond (usec) spark pulses of approximately constant orslowly decaying amplitude, and preferably designed such that if thefirst spark pulse misfires the coil will permit the recharge circuit toraise the primary, and hence secondary voltage of the second pulse to ahigher value.

Another feature of the present invention to design the capacitance (Csc)of the secondary winding of the coil invention so that it is of lowvalue, e.g. 20 to 40 picofarads (pF), by making use of the coilinvention design principles and by utilizing low dielectric constantmaterial in the secondary winding.

Another feature of the present invention is to minimize both thesecondary (output) coil capacitance Csc and the secondary AC(alternating current) resistance by utilizing the new coil designcriteria to wind the secondary with an essentially square winding or awinding with more layers Nl than turns Nt per layer.

Another feature of the present invention is to provide a variable turnsNti per ith layer where over some range of values of layers Ntidecreases to increase the clearance of the higher voltage turns from the(ground) ferrite core sidewalls.

Another feature of the present invention is to make use of the coilsecondary winding capacitance Csc for effective sparking (capacitivespark) by designing the high voltage lead connecting the coil outputterminal to the spark plug to lower the frequency of transmission of thecapacitive spark to 5 to 15 Megahertz (MHz) so that it is delivered withsmall attenuation to the spark gap while energy flowing above 30 MHz isstrongly attenuated.

Another feature of the present invention is to contain the abovementioned high voltage lead in a grounded shield terminating at the coilcore outer surface and at the plug shell for low EMI.

Another feature of the present invention is to make use of the preferredaxially side-by-side coil winding and to use two layers of primarywinding such that the beginning and end of the primary winding are inclose proximity of each other.

Another feature of the present invention is to use the coil as part of aCD circuit with the discharge circuit mounted on or in close proximityof an outer surface of the core on which the primary winding is woundwith preferably a two layer primary winding such that the two ends ofthe winding locate very closely to the discharge circuit and require alength of preferably no more than one to two inches of primary windingwire to make the connection to the discharge circuit.

Another feature of the present invention is to incorporate the preferredaxially side-by-side windings essentially in each half of a core withone or more similar outer diameters but otherwise differing dimensionsas dictated by the new coil design criteria.

Another feature of the present invention is to use a pot type core suchthat two layers of wire are used in the primary winding which start andterminate at one end surface of the pot core half and the secondary highvoltage end of the winding is terminated at the opposite end surface ofthe pot core.

Another feature of the present invention is to use wire for the coilwhich is chosen and oriented such that the AC resistance of the wire atits principal operating frequency is preferably less than a factor oftwo of its DC (direct current) resistance, such as Litz wire of suitablestrand size.

Another feature of the present invention is to use a Litz wire for theprimary winding and a suitable wire in the secondary winding with adiameter preferably equal to about one half the skin depth as defined bythe operating frequency of the CD spark discharge oscillation frequency,which is preferably about 10 kHz (kilohertz) for a skin depth of about0.030 inches for copper. and a diameter of about 0.015" for thesecondary winding wire.

Another feature of the present invention is to use a solid conductorwire in the secondary winding whose copper diameter is between one thirdand two thirds the skin depth, i.e. between 0.010 and 0.020 inches for10 kHz operating frequency.

Another feature of the present invention is to wind the secondary wirein an essentially rectangular winding cross-section whose larger windingdimension is essentially parallel to the leakage magnetic field producedby the primary winding.

Another feature of the present invention to design the coil on the basisof the Doubling principle, i.e. the high efficiency low turns ratiovoltage doubling principle, to be used in a MPCD circuit with primarycircuit capacitor Cp of about 5 microfarads charged to preferably about350 volts, preferably used in conjunction with a recharge circuit withcapacitance Ce one quarter to one half the value of Cp and rechargecircuit inductance Le of about 20 millihenries (mH) and total secondarycircuit capacitance Cs preferably no more than 100 pF containedprincipally in the spark plug (and coil for distributorless ignition)with the spark plug preferably having a toroidal gap of the electricfield focussing lens (EFFL) type.

Another feature of the present invention is to design the coil inventionsuch that it provides a positive polarity high voltage output versus theconventional negative polarity in order to minimize plug fouling.

Another feature of the present invention is to use the coil with atoroidal gap focussing lens type plug (EFFL plug) with a firing endbutton tip made of small diameter, e.g. 0.25" to 0.30", erosionresistant material such as Tungsten-Nickel-Iron, Tungsten-Nickel-Copper,or others, and the plug ground ring made up of similar material, to beable to withstand the higher spark pulsing power made possible by thepresent high efficiency coil design.

Another feature of the present invention is to use the coil with an EFFLplug with preferably a plug capacitance Csp of about 40 pf and a minimumoutput coil capacitance Csc.

Another feature of the present invention is to design the firing end ofthe EFFL plug such that it provides an approximately 0.1" spark gapwhich is at an approximately 45 degree angle to the vertical axisdefined by the plug length to minimize the chances of plug fouling.

Another feature of the present invention is to use the coil invention inconjunction with an MPCDRC ignition system using low forward drop SCRsas the spark pulsing switches of one volt forward drop or less at 100amp current, and capable of producing closely spaced multiple sparkpulses of short oscillation period of 80 to 120 microseconds, broughtabout by a speed-up shut-off circuit which applies a negative bias tothe SCR trigger gate during SCR firing to shorten the SCR's recoverytime and provide an optimized ignition pulse train for the presentinvention.

Another feature of the present invention is to advantageously use theMPCDRC ignition system and an EFFL plug with the present coil inventionand provide many spark pulses per ignition firing, e.g. 10 to 20 at lowRPM, dropping to preferably about 3 closely spaced (e.g. 250 usec)pulses at 6,000 RPM.

Another feature of the present invention is to supply enough such sparkpulses per firing to ignite at least about half of the toroidal volumeof the EFFL plug at low RPM engine operation.

Another feature of the present invention is to provide a variable sparkpulse timing with gradually increasing time between pulses withsubsequent pulses, increasing by a factor of about two, i.e. initialtime between pulses of, say, 250 usec which increase to 400 usec at theend of the tenth pulse, and to say 500 usec at the end of the 15th pulseif such a long pulse train is used.

Another feature of the present invention is to use such a variable, longduration pulse train to ignite a large volume.

Another feature of the present invention is to make the core halves ofbutted "E" cores with preferably one similar outside dimension and theprimary comprised of thin, low loss laminations and the secondary coredesigned with a smaller center post diameter so that it provides a largeheight of its winding window.

Another feature of the present invention is to produce an off-setbetween the primary and secondary cores by, for example, using a largerlamination stack in the primary core in a laminated type core, so thatthe off-set allows for adjustment (increase) of the primary leakageinductance Lpe (and primary inductance).

Another feature of the present invention is to make the core of a doubleinternal diameter single "E" core or pot core with an "I" bar (for an"E" core) or cylindrical cap (for the pot core).

Another feature of the present invention is to use a separate outercasing for the core material of a pot core type design which is noteasily breakable, e.g. plastic with ferrite loading, NiFe or SiFe metaltape wound in cylindrical tubular form, and others, to be used to moreadvantageously select the dimensions of parts so that structural factorscan be neglected, i.e. so that thin outer tubes can be used, and byusing high saturation flux density metal tape to be further able to makethe outer sections of even a thinner wall.

Another feature of the present invention is to use the coil invention ina distributor type ignition of the MPCDRC type in which more than one(set of) SCR(s) is provided which are fired alternatively with eachignition trigger to relieve the thermal stress on the SCRs at high RPMand in engines with many cylinders.

Another feature of the present invention is to provide one set of SCRsper two to four cylinder of an engine, so that, for example, two setsare provided for a standard V-8 engine, three to four sets for a highspeed 12 cylinder engine, and so on.

Another feature of the present invention is its special suitability forassuring ignition under otherwise problematical conditions imposed bylarge volumes, cold ambient, alcohol fuels, engine wear, and non-optimumtuning and the like.

Another feature of the invention is its contribution, generally, totransformer arts, apart from the ignition context.

Another feature of the present invention of the side-by-side windingplacement is to use two different magnetic materials for each windingcore half, a low loss (preferably ferrite) material for the half inwhich the primary wire is wound and a low cost (generally higher loss)high magnetic saturation material, e.g. Silicon Iron for the half onwhich the secondary winding is wound.

Another feature of the present invention using separate windings is todivide into two parts the separate high leakage inductance Lpe primarywinding of the coil, a first part (Lpel) that is coupled to thesecondary winding through either very low leakage concentric windings orside-by-side windings comprising the primary winding of a compacttransformer (coil), and a second part that is contained in a separatecore comprising a choke of leakage inductance Lpe2, wherein generallyLpe2 is greater than Lpe1.

Another feature of the present invention is to provide two separateprimary windings of leakage inductance Lpe1 and Lpe2 to decouple part ofthe primary leakage magnetic flux from the secondary winding to minimizesecondary winding AC losses and losses of the core supporting thesecondary winding so that smaller, lower cost, high magnetic saturation,higher loss material, e.g. Silicon Iron (SiFe), can be used for thecompact coil.

Another feature of the present invention is to provide simple, low costforms of distributorless ignition by utilizing a single leakage choke ofinductance Lpe2 with the required number of low leakage inductancecompact coils (of leakages Lpe1i) which can be made very small and cheapthrough the use of SiFe laminated magnetic core material.

Another feature of the present invention is to utilize an alternativeform (topology) of discharge circuit made possible by the presence ofthe large (isolation) choke of the preferred recharge circuit to developa particularly simple form of distributorless ignition system.

Another feature of the present invention is to use the advantages of thetwo part primary winding coil structure to build a particularly smallcompact coil with high saturation flux density core material, such asvery small particle sized Powdered Iron or Silectron or other materialwhich can be easily formed into shape, wherein said small coil can bemounted over a spark plug for a particularly compact overall design.

The objects of the invention include realization of the foregoingfeatures.

Other features and objects of the invention will in part be obvious andwill in part appear hereinafter; the foregoing enumeration is notexhaustive. The invention accordingly comprises the apparatus possessingthe construction, combinations of elements and arrangements of parts,and the process including the several steps and relation of one or moreof such steps with respect to each of the others, exemplified in thefollowing detailed disclosure and the scope of the application of whichwill be indicated in the claims.

For a fuller understanding of the nature, features, and objects of thepresent invention reference should be made to the following detaileddescription taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an idealized view, partially in block diagram and partiallyschematic, of a preferred embodiment of a complete system designed formore optimally using the present coil invention for internal combustionengine applications, including an energy delivery circuit of thecapacitive discharge type with the preferred recharge circuit andpreferred EFFL spark plug.

FIGS. 2a and 2b are the primary voltage and recharge current waveformsrespectively of a preferred MPCDRC ignition using the present coilinvention.

FIGS. 3a and 3b are the primary voltage and recharge current waveformsrespectively of a preferred MPCDRC ignition using the coil inventionwhich is further designed in conjunction with the spark pulse timing toprovide a higher voltage second spark pulse should the first pulse notfire the spark gap.

FIG. 4 is a cross-sectional side view of the coil invention featuringthe two differing core halves containing each winding separately andshowing magnetic flux density lines.

FIG. 5 is a side view cross-section of a preferred embodiment of thecoil invention using a modified E-type core made of ferrite, thinsilicon iron or nickel-iron laminations, or other material.

FIG. 5a is a table of preferred dimensions for the preferred coil designof FIG. 5.

FIG. 6 is another side view cross-section of the coil design of FIG. 5including components of a CD circuit which are preferably used with thecoil.

FIG. 6a is a table of preferred dimensions for the preferred coil designof FIG. 6.

FIG. 7 is a side view drawing of a preferred embodiment of the coilinvention featuring a pot core comprised of two different magneticmaterials, a single central ferrite core piece with single ferrite endcap, and preferably non-ceramic outer material such as metal tape (SiFe,NiFe) wound in a cylindrical tube or plastic or other semi-rigid ferriteloaded material comprising a tube for the return magnetic flux.

FIG. 7a is a table of preferred dimensions for the preferred design ofFIG. 7 which is particularly compact and suitable for a distributorlessignition system.

FIG. 8 is a detailed side-view drawing of an approximately to-scaleembodiment of the coil invention in a pot type core using athree-sectioned, low output capacitance secondary winding.

FIG. 9 is a drawing of a possible compact orientation of a CD circuitused with the coil invention.

FIG. 9a is a fragmentary, partial view of a positioning of an SCR anddiode of a CD circuit used with the coil invention.

FIG. 10 is a preferred spark plug wire to be used especially with adistributorless form of the coil invention.

FIG. 11 is an equivalent circuit of the coil and the secondary circuitshowing features of the preferred spark plug wire of FIG. 10.

FIG. 12 is a secondary circuit attenuation or resistive impedance curvefor the preferred spark plug wire of FIG. 10.

FIG. 13 is an approximately to-scale drawing of a side viewcross-section of a preferred embodiment of the coil invention designedfor a pot core.

FIG. 13a is a table of preferred dimensions for the preferred coildesign of FIG. 13.

FIG. 14 is a half side view cross-section of a preferred embodiment ofthe coil invention showing an alternative means of constructing themagnetic core and winding the secondary turns.

FIG. 15 is a variant of a standard form of high leakage inductance coilwinding modified to more optimally use the design criteria of thepresent invention.

FIG. 16 is a cross-sectional view of a preferred embodiment of an EFFLtype spark plug suitable for use with the present coil invention whenused as part of an MPCD ignition system.

FIGS. 16a, 16b are a fragmentary cross-sectional views of preferredembodiments of the spark firing end of the spark plug of FIG. 16.

FIG. 17 is an ignition coil featuring different materials for the twohalves of the core comprising the core of the coil.

FIG. 17a is an ignition coil in which the major part of the leakageinductance Lpe is provided by a separate external choke whose corematerial is preferably low loss material such as ferrite and transformersection being preferably of Silicon Iron or other low cost highsaturation flux density material.

FIG. 18 depicts a distributorless form of ignition discharge circuit inwhich a single external leakage choke serves for two or more compacttransformer coils.

FIG. 19 depicts an alternative topology of spark ignition capacitivedischarge circuit now made possible as a result of the presence of anisolation choke (of a recharge circuit).

FIG. 19a is a preferred embodiment of the alternative capacitivedischarge circuit (ACD circuit) with a separate external choke placed ina preferred position.

FIG. 20 is a circuit drawing of the preferred distributorless ignitionin which one discharge capacitor and one external leakage inductor serveseveral compact ignition coils.

FIG. 21 is an approximately half scale schematic of an actualdistributorless ignition of FIG. 20 for a four cylinder engine.

FIG. 22 is an approximately half scale schematic of a particularly smallcompact coil for mounting directly over a spark plug.

FIG. 23 is an approximately full scale drawing of a top view of apreferred embodiment of a coil assembly of a distributorless ignitionfor a four cylinder engine.

FIGS. 23a, 23b are full scale drawings of side views of preferredcompact coils made from laminations (scrapless design) and the singleleakage inductor made from ferrite material.

FIGS. 24a, 24b are top and side views of the core of preferred compactcoils made of ferrite or other shapeable material.

FIG. 25 is an approximately full scale drawing of an end view of acompact coil showing a preferred high voltage tower design.

FIG. 25a is a fragmentary top view of a compact coil showing analternative placement of the high voltage tower.

FIG. 26 is an approximately full scale side view of a coil assembly ofthe distributorless ignition of FIG. 23 depicting a preferredsandwiching design for holding the parts.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of a preferred ignition system circuit of thecapacitive discharge (CD) type 19 which can advantageously make use withthe coil invention 3, which is shown in a schematic partial view form.The ignition is typically powered by a battery 11 of voltage VB(typically 6, 12, or 24 volts) and a DC-DC power converter 12 used toraise the battery voltage to a more usable value Vp, typically in therange of 200 to 600 volts. Preferably, converter 12 is of the highefficiency type disclosed in U.S. patent application Ser. No. 179,953 oran improvement thereof. The system includes controller means 13 tocontrol both converter 12 and the discharge circuit 19, and preferablyalso includes a recharge circuit 14 of the type disclosed in U.S. patentapplication Ser. No. 131,948, connected at the output of the converter12. Spark plug means 16 is preferably of the annular gap type disclosedin the above patent application. Essentially, the coil invention wasdeveloped to provide an improved coil design for the optimized ignitioncircuit disclosed in above patent application 131,948, and to furtherimprove the performance of the ignition.

For the purpose of specification of the various parameters and tofacilitate the disclosure, the following definitions are made:

"equal to X" implies X+ or -10% of X;

"approximately (equal to) X" implies X+ or -25% of X;

"about (equal to) X" implies X+ or -50% of X;

"of the order (of magnitude) of X" is as per convention to be a valuebetween 0.1 of X and 10 times X.

To further facilitate the disclosure, discharge capacitor 4 of the CDcircuit 19 and recharge capacitor 10 will be taken to be 400 voltcapacitors with values of about 6 uF and 3 uF respectively (charged toapproximately 350 volts), it being understood that CD circuits in partare designed according to their total capacitive stored energy, which inthe present application is preferably about 1/2 joule, designating ahigh power, high energy system capable of utilizing the voltage doublingprinciple first disclosed in U.S. Pat. No. 4,677,960. Thus, if a similarsystem is designed with, say, 600 volt capacitors, then for the samestored energy one would reduce the size of the capacitors to about 3 uFand 1.5 uF respectively. Likewise, in cases where a design parameter isproportional to the voltage Vp to which capacitor 4 is charged, e.g.number of turns Np of primary winding 1 of coil 3, the value of thatdesign parameter will accordingly be modified (increased proportionallyfor Np with the voltage Vp).

In operation, capacitor 4 is initially charged to a voltage Vp ofapproximately 350 volts by means of the DC-DC converter 12. Uponignition firing, controller 13 applies trigger signals to one or moregate 5a of preferably one or more SCR switching means 5 to dischargesaid capacitor across primary winding 1 of coil 3. Current flowssinusoidally through capacitor 4 and primary winding 1 with a preferredperiod of about 100 usecs, initially through SCR 5 and then throughdiode means 6, with SCR 5 preferably recovering at the end of the firstapproximately 100 usec period. Snubber means comprising capacitor 4a andresistor 4b are preferably provided to safeguard recovery of SCR. Diodemeans 4c may be used as part of the snubbing circuit to reduce snubberlosses and resistor 4b limits the snubber current to the SCR upon SCRturn-on. Other lossless snubber means may also be used. Typically,capacitor 4a is 0.05 to 0.2 uF and resistor 4b is a few ohms or lessi.e. can be eliminated. Fast SCR turn-off circuit of the type disclosedin detail in patent application Ser. No. 131,948 is preferably used tospeed up the recovery of SCR means 5.

Upon SCR triggering, output terminal 7a of secondary winding 2, of turnsNs and of turns ratio N (N=Ns/Np) of approximately 50, rises to avoltage sufficient to breakdown spark gap 17a of plug 16 and to producea sinusoidal spark current of preferably peak value Ip of about 2 ampsand frequency of about 10 kilohertz (kHz), where:

    Ip=2*pi*f*Cp*Vp                                            [1]

where

pi=3.142;

f=frequency of oscillation of discharge circuit 19,

f=1/[(2*pi)*SQRT(Lpe*Cp)];

Cp=capacitance of discharge capacitor 4;

Lpe=leakage inductance of primary winding 1.

The symbol "SQRT" is defined to mean the "square root of" the quantityfollowing it.

For the 10 kHz operation and the preferred value Cp of approximately 6uF, Lpe should have a relatively high value (given the small number ofprimary turns Np) of approximately 45 microhenry (uH), which is one ofthe requirements that led to the development of the present coilinvention. In addition, the ignition should be preferably operated in amulti-pulsing or multi-strike mode in conjunction with the rechargecircuit 14, made up of capacitor 10 of capacitance Ce equal to 1/4 to1/2 the value (Cp) of capacitor 4, choke inductor 9 of inductance about20 mH, and diode 8.

A key feature of the coil invention is based on the recognition that theopen circuit, high voltage (e.g. approximately 30 kV) coil operatingcondition is different from the short circuit sparking operatingcondition, which leads to a preferred side-by-side windings 1 and 2around the core 3a shown schematically in the figure. Moreover, the coildesign requires minimization of coil secondary output capacitance 7,both from the perspective of coil core 3a saturation and peak outputvoltage Vs. Spark plug 16 preferably has a moderate capacitance ofapproximately 40 picofarads (pf) and annular and/or forward firingaverage spark gap 17a of about 0.1 inch with respect to the cylinderhead 17 or piston 17b connected to the chassis ground 18.

For clarity, it is pointed out that while the coil invention to bedisclosed is a well defined, stand alone device, it provides greatbenefit when particularly used in conjunction with the circuit shown inFIG. 1, i.e. the circuit and coil complement each other. This circuitwas disclosed as a circuit for more optimally providing the benefits ofthe new approach to ignition which also advantageously makes use of thepresent invention, which circuit is disclosed in patent application Ser.No. 131,948 and in the 1989 SAE paper No. 890475, "A New Spark IgnitionSystem for Lean Mixtures Based on a New Approach to Spark Ignition", byMichael A. V. Ward.

FIGS. 2a and 2b depict the primary voltage waveforms 21, 22, and 23, andthe recharge current Ire waveforms 24 and 25 of the preferred embodimentof the ignition circuit of FIG. 1 operated as a multi-pulsing systemdefined herein as an MPCDRC ignition system. Preferably, as stated, thedischarge period Te is approximately 100 usecs and the complete singlepulsing period Ti (where the subscript "i" represents the ith pulse) istwo to five times Te, preferably approximately three times(approximately 300 usecs) for the first few pulses and preferablygradually increasing to, say, 500 usecs after the tenth pulse (if ten ormore pulses are used in a single ignition firing train, as may bepreferred at low RPM engine conditions). Typically, as a result of therecharge circuit (14) operation initial voltage Vp2 of the second pulsewill be approximately equal to or greater than Vp1.

In operation, the recharge circuit 14 conducts current Ire through choke9 during the 100 usec discharge period Te, designated as 24a, storingmagnetic energy in the choke 9, which is subsequently delivered (phase24b) to capacitor 4 such that preferably the current Ire has reachedzero at approximately the time periods Ti, as would be achieved with thevalues of the various parameters already disclosed.

FIG. 3a depicts the primary voltage waveforms 26 and 27 for theparticular case where the first pulse of peak primary voltage Vpoc1 isnot high enough to produce sufficient secondary voltage to fire the gap,and wherein the primary inductance Lp is selected such that the misfirewaveform 26 of period Toc is less than T1 to allow recharge of capacitor4 before the second pulse, preferably to an even higher voltage Vpoc2than the normal voltage Vp2 to insure firing of the gap on the secondpulse. Since the discharge period Toc is defined by the primaryinductance Lp and not the primary leakage inductance, then therequirement is that Lp/Lpe be less than (T1/Te)**2, preferably less thanby about 50 usecs. At the same time, Lp is preferably approximately tentimes Lpe to provide a high coupling coefficient k, e.g. k=0.95, where:

    k=SQRT[1-(Lpe/Lp)]                                         [2]

Values of 45 uH and 400 uH for Lpe and Lp respectively give a period Tocof 300 usec for Te of 100 usec, which is satisfactory for an initialperiod T1 of 350 usec (which may preferably be set somewhat higher thanthe next few periods T2, T3, T4, which could be set at, say, 250 to 300usecs). However, because the core may part saturate during the lowerfrequency misfire period, measured period Toc may be less thantheoretical, which can be taken to advantage by not requiring Lp to beas small as otherwise is required (and hence k can be higher).

FIG. 3b depicts the first two recharge current waveforms 28 and 29,particularly showing the longer initial period 28a corresponding to theperiod Toc and the short (about 50 usec) period 28b. Note that for thecase wherein waveforms of recharge current Ire are back to back, i.e. nozero current dead time exists during the multi-pulsing period, diode 8may be eliminated.

FIG. 4 depicts a cross-sectional side view of a preferred embodiment ofthe coil invention featuring the two differing core halves 31 and 41containing respectively the primary 1 and the secondary 2 windingsseparately and showing magnetic flux density lines 30, 30a, 30aa, 30ab,30b. In this preferred embodiment the primary winding 1 comprises twolayers of about 10 turns total of preferably Litz wire wound around acenter post 32 of a pot core, an E type core, or similar core, and thesecondary wire comprises wire 2 wound on the other center post 42 withabout 500 turns (turns ratio N of approximately 50 for assumed use ofthe Doubling principle). Diameter of wire of secondary winding 2 isabout one half the skin depth (for the operating frequency ofapproximately 10 kHz) and wound in an approximately square winding andpreferably, if practical, with a maximum ratio of height h1 to width ofwinding 1t so as to minimize AC losses and winding capacitance. A gap 38may be included to allow for adjustment of the primary inductance Lp toa value approximately ten times Lpe as disclosed. Note that in this andother figures the primary and secondary windings are wound in thewindows 33 and 43 respectively, and are generally only shown on one halfside, it being understood that in general the windings are symmetricalabout the center line CL of the magnetic core 3a.

A main feature of the invention was to recognize that by providing alarger primary winding center post 32 (versus post 42) the magnetic fluxlines 30 will preferably return across gap 38a to provide most of theleakage inductance Lpe (which is contained internal to the core volume)with flux lines 30b representing the remaining externally lying leakageflux lines. In this way it is possible to minimize the diameter of core42 which carries the secondary winding and thus provide a maximum heighth1 for a given overall core diameter D. Thus, the large number of layersof the secondary wire 2, e.g. thirty layers of #28 wire with hold-offvoltage interleaving, can be accomodated, which also minimizes thenumber of turns per layer and the effect of the leakage flux lines 30 onthe AC resistance of the secondary winding 2. For a preferred thirtythree layer winding and a 33 kV maximum secondary output voltage, themaximum voltage between layers is an average of 2,000 volts which can behandled by preferably using heavy, e.g. quad, coated magnet wire for thesecondary winding 2 with a few mils of insulation between layers. Inaddition, the secondary coil winding output capacitance Csc is minimizedwith the large number of layers.

Flux lines 30a cross gap 38 into secondary post 42 (becoming flux lines30aa) to couple to the secondary winding 2. In turn, flux lines 30ab areinduced tending to cancel flux lines 30aa and 30a to minimize the fluxdensity in core 42, especially under spark firing conditions (closedcircuit secondary winding 2).

The invention is based in part in separating out the spark firing orclosed (secondary) circuit conditions from the open circuit condition.In the closed circuit condition, almost all the (uncancelled) flux linesare carried in the primary core 31 across gap 38a, so that in designingthe primary winding based on losses and saturation flux density one cantreat the primary as a stand alone choke of inductance equal to theleakage inductance and calculate the magnetic flux density B accordingto:

    B=Ip*SQRT[Lpe*Meff/Vm]                                     [3]

where Ip, the peak primary current has already been defined;Meff=Lpe/Lpair, where Meff is the effective permeability, Lpe is theleakage inductance, Lpair is the inductance of the primary winding withthe core removed, and Vm is the primary core volume.

Once the primary core 31 and winding is specified based on the aboveformulation, then it will automatically satisfy the open circuitcondition which produces a significantly lower magnetic flux density inthe core because the open circuit frequency foc of oscillation is muchhigher than the closed circuit or sparking frequency fcc (of thepreferred approximately 10 kHz). Typically, for the present invention,foc=4*fcc, as will be shown.

The design of the secondary core 42 is based on the open circuitcondition. Because of foc's higher value (compared to fcc), secondarypost 42 diameter can be made smaller, although the amount it can bereduced is not a simple function and will be disclosed with reference toFIG. 13, representing a design based on low saturation flux-densitymaterials, i.e. ferrite material. The amount it can be reduced islimited by the saturation flux density Bsat of the secondary windingcore material. For a high Bsat material, such as Silicon Iron, NickelIron, etc, the limitation is one of losses and not saturation, and sincelittle energy is associated with the initial open circuit high breakdownvoltage, one is free to pick the diameter to a suitable small value.

FIG. 5 is an approximate to-scale design based on a high Bsat materialand is presented as a preferred embodiment and as a case whichdemonstrates features and advantages of the coil invention. The drawingis a partial top view cross-section of a preferred embodiment of thecoil invention using a modified E-type core made of thin silicon iron(SiFe) or nickel-iron (NiFe) laminations, or other material, includingferrite. For the case of laminations, preferably, the laminations are 2to 6 mil thick (1 mil=0.001") to minimize core losses at the preferredfrequency fcc of approximately 10 kHz (which may in this case oflaminations be lowered to, say, 8 kHz). In this and in the followingfigures like numerals denote like parts with respect to the previousfigures.

FIG. 5a is a table of preferred dimensions for the preferred coil designof FIG. 5, the dimensions being "approximate" as per the definition.They can be adjusted depending on whether the application is for adistributor type or distributorless system (where smaller dimensions arepreferred in the latter).

In this preferred embodiment, twelve turns of primary winding (Np) ofpreferably Litz wire are used in two layers. Given the window 33 widthdimension W1 of approximately 0.3 inches and the length 12 ofapproximately 1.0 inches, twelve turns of 0.15 inch diameter Litz wire(made up of #30 wire strand) is suitable, giving a very low resistanceof approximately 5 milliohms and a maximum flux density Bmax given bythe alternative formula:

    Bmax=Vp/[2*pi*f*Np*A]                                      [4]

where A (or Ap) is the primary core cross sectional area. For the aboveparameters and further assuming:

f=fcc=10 kHz

Vp=350 volts

gives a value for Bmax of 0.72 Tesla, which is approximately half ofBsat for NiFe and less than half of Bsat for SiFe.

The core losses are calculated in the normal way although the corevolume is taken as that of the primary core half 31. For 2 to 4 mil NiFecore material the core losses may be acceptable for a high efficiencycoil, defined as a coil whose core and wire (power) losses are less thanthe spark gap power dissipation Parc. For (2 to 4 mil) SiFe the corelosses may be too high and may be reduced by increasing the windinglength 12 and the number of primary turns, to say 15 turns, which alsoincreases the leakage inductance Lpe. Value of capacitor 4 may bereduced, say, 20%.

The secondary core is designed to provide a winding window with heighths of 0.5 inch (and insulating layer of 1/8 inch, for a total dimensionW2 of 5/8 inch) and a winding width 1s of 0.45", assuming 1/8 inchinsulating layers on each side. Assuming quad coated #28 wire (diameter0.016 inches) and 0.004 inch insulation between layers, for a 600 turnsecondary winding (turns ratio N of 50 for Np=12), one can easilyaccomodate 24 turns per layer and 25 layers, for low AC losses and lowoutput capacitance Csc.

The dimensions given in FIG. 5a are consistent with the above disclosureexcepting that the two legs of primary core 31 are shown as 0.45 versus0.5 inches, or 10% less than half of diameter a2, arrived at on thebasis of experimental measurements.

FIG. 6 shows the other side view of the coil excepting that it includesa high voltage tower 48 with the secondary high voltage end of the wire47a brought out as shown to terminal 49a. In addition, in thisembodiment the secondary core section 42a is off-set from the primarycore section 32a to accomodate the discharge circuit made up ofcapacitor 4 and the other components designated in total as 60. Typicalapproximate dimensions are given in FIG. 6a.

One of the features of this coil design is its higher efficiency (for agiven volume), as compared with the high efficiency coils disclosed inU.S. patent application Ser. No. 131,948. Taken with the more efficientspark delivery circuit which includes the recharge circuit 14 and thepreferably high efficiency power converter disclosed in patentapplication Ser. No. 179,953, one can operate the ignition with a largernumber of pulses per spark firing, e.g. 8 to 16 pulses at low RPMwithout undue battery current draw.

FIG. 7 is an approximately to-scale cross-sectional side view of apreferred embodiment of the coil invention in a pot core configurationwith the secondary post 42b area As approximately one half the area Apof the primary winding center post 32b and with typical dimensions foran especially compact design (e.g. for a distributorless ignition) givenin FIG. 7a. This design is based on the example worked out in "Case 6"with reference to FIG. 13 wherein a high frequency of approximately 20kHz is assumed for the discharge frequency fcc.

In this design is depicted one of several possible practical designs formanufacturing the pot core, wherein center posts 42b and 32c and the endplate 32c of the primary winding side are made of one easily moldableferrite core piece. The secondary winding cap 42c is a separate piece,as are the outer cylindrical tube sections 36 and 46. This design lendsitself to designing the outer section 46 of thin material based on therequirements of the magnetic design, as presented with reference to FIG.13, and not on structural principles, which would require sections 46and 42c to be of thicker wall to prevent breakage.

Preferably, material comprising cylindrical tubular sections 36 and 46be of non easily breakable material, including and not limited toplastic loaded with ferrite to give as high a permeability as practical(e.g. relative permeability of about 100), metal tape wound to theappropriate thickness, recognizing that very thin layers (e.g. 1/4 to1/2 that given in the table of FIG. 7a) may be possible if SiFe or NiFetape is used because of their very high values of saturation fluxdensity Bsat.

FIG. 7a, as already stated, gives suitable design values for a smallcoil design. By following the principles presented with reference toFIG. 13, one can modify these parameters, the main feature beingpresented here is the novel way of fabricating the core, including theapplication of more than one magnetic material being used to advantage.

FIG. 8 is a detailed drawing of an approximately to-scale embodiment ofthe coil invention in a pot type core using a three-sectioned, 2a, 2b,2c, low output capacitance secondary winding wound on a dielectric frame45. Such a winding has an inherently higher AC resistance and istherefore more suitable for Litz wire.

In this design, the dimensions 11, 12, and D are similar to those ofFIG. 5 while dimensions 13, 14 are somewhat longer as is diameter ofsecondary center post 42, which is assumed to be of ferrite material inthis embodiment. The two core halves 31 and 41 (and end cap 51) are heldtogether by nut and bolt section 35, 34, 44, 28. The two layer primarywinding 1 is brought out at the back surface with leads 1a, 1b. Thesecondary winding is conveniently brought out through tower 48 by meansof lead 47 which is connected to output tip 49. Secondary ground return50 is brought out adjacent to the tower and may be terminated on theground plate 51. In such side-by-side bringing out of the secondary wireends 47 and 50, the secondary output capacitance Csc of the coil isavailable for producing a capacitive spark without being impeded (whichwould otherwise occur if ends 47 and 50 were brought out throughseparate holes in the magnetic core material).

This cylindrical pot core design, as the one depicted in FIG. 7,features particularly low EMI and compact design and may be particularlysuited for distributorless ignition, especially if the overall outputcapacitance Cs can be kept at, say, 75 pF (30 pF for coil, 25 pF for thewire, 20 pF for the spark plug), and even lower capacitance Cs (e.g. 50pF) if the coil is directly mounted on the spark plug.

FIG. 9 depicts a typical discharge circuit layout designed toconveniently mount to the back side of primary core 31 (see FIG. 8) tominimize the length of the primary wire 1. Conductor sections 8a and 8bcarry the high voltage and return to the 350 volt supply, preferablythrough the recharge circuit 14. Wire 5a is the gate of the SCR 5, andcomponent 6 is tab type high current diode means. Side-by-side mountingof the SCR(s) 5 and diode 6 shown makes for good layout of their anodeand cathode terminals. Capacitor 4 is preferably of rectangular shape(of preferably 3 to 6 uF value) with the larger cross-section shown inthe figure.

FIG. 9a is a fragmentary partial view of the discharge circuit of FIG. 9in which the SCR(s) and diode are mounted vertically along conductor 8aawhich also serves as a heat sink. While not specifically shown, SCR 5and diode 6 anode and cathodes can be reversed as per the layout of FIG.1 so that the heat sink tab of the case of the devices are at groundpotential, the output of converter 12 is at a negative polarity, diode 8(if present) is reversed, and isolated trigger means are provided forSCR gate 5a. Magnetic sense of primary winding should be accordinglyreversed to provide the correct polarity of the high voltage output Vsfor spark gap breakdown.

With regard to the "correct" high voltage polarity, it has beendiscovered for the present application of a preferred spark plug withannular gap, a positive, not conventional negative high voltage initialbreakdown polarity Vs is preferred because of the reduced fouling of theplug tip insulator with positive polarity.

With reference to FIGS. 8, 9, 9a, it should be noted that the primaryleads 1a, 1b could also be brought out on the opposite side of thatshown in FIG. 8 along the notched corner 36a of the outer core section36 of the primary (winding) half core 31 along a lengthwise, ifnecessary, notched section of the outer section 46 of the secondary halfcore 41. Such notched length, for example, is standard in the Ferroxcubecore part number 6656PL00-3C8. In such an embodiment, the dischargecircuit of FIG. 9 would preferably be placed on the surface defined byplate 51 near the high voltage tower 48 to make for a particularlycompact design.

FIG. 10 depicts a preferred design of spark plug wire particularly wellsuited for use with a distributorless form of ignition in which the coilis directly connected to the spark plug 16. Spark plug wire 52 has aground casing 53, preferably of flexible mesh type and high voltageinsulation 54 preferably of low dielectric constant to minimize the wirecapacitance to preferably keep it below 50 pF. The center conductor ispreferably wound in a helix as is commonly done with EMI suppressionwire, excepting in this case the two ends of the helix winding 55a, 55bmay comprise more tightly wound sections around an air cores 56a, 56bwhich do not saturate. Central winding section 57 preferably is woundaround ferrite core material 58 which is preferably powdered highfrequency ferrite material encapsulated in rubber or other preferablyflexible material used for such purposes. The outer casing is terminatedin threaded tubes 51b, 51c or tubes comprised of spring type materialwhich can be mounted on the spark plug shell and onto a protrudingsection 51a of the ground plate 51 which is mounted (and grounded) ontothe face of the core secondary 41 of the coil. Clips 59a, 59b areprovided for connecting the center high voltage carrying conductor.

Such a spark plug wire shown in FIG. 10 may also be used in anunshielded form as a spark plug wire for distributor ignition or as ashielded King lead (coil wire) in a distributor type ignition withunshielded spark plug wires.

FIG. 11 depicts an equivalent circuit of the coil 3 and its secondarycircuit including the wire of FIG. 10, and a spark plug of capacitanceCsp (16a) and spark gap 17a. In this preferred embodiment, use is madeof the coil capacitance Csc (7) and the distributed capacitance (notshown) of the wire 52 to allow the energy stored in them prior to sparkbreakdown to be delivered with minimum attenuation to the spark gap.These capacitances are designed preferably to be of low value e.g. 20 to40 pF each, but when taken together with the plug capacitance provideapproximately in total 120 pf, a design value preferably not to beexceeded as it will otherwise significantly compromise the peak outputvoltage, as discussed in detail with reference to FIG. 13.

In U.S. patent Ser. No. 4,774,914, FIG. 2a, there is disclosed the highfrequency spark currents due to the discharge of the plug capacitanceCsp, and the moderate frequency spark current (5-30 MHz in the presentcase) due to discharge of the coil (Csc) and wire distributedcapacitances which are moderated by interposing the inductances 15a,15b, 15c. The total wire inductance, shown as air core inductances 15a,15c (of values Ls1) and ferrite core inductance 15b (value Ls0) of totalvalue of about 10 uH, act to tune and lower the frequency of dischargeof coil capacitance to 5-15 MHz and to lower the peak currents to about20 amps. Inductances 15b and 15c act to tune the distributed capacitanceto a somewhat higher frequency value but preferably below 30 MHz.

FIG. 12 depicts the preferred secondary circuit attenuation or resistiveimpedance curve of the combination of inductances 15a, 15b, 15c of thepreferred wire of FIG. 10 as a function of frequency, where inductance15b uses high frequency core material, e.g. Ceramic Magnetics materialC2075, Fair-Rite Material 65, etc. As is seen, in the desired frequencyrange of 5-15 MHz, the attenuation is very low, approximately 1 ohm, thetypical maximum preferred value of the secondary wire DC to lowfrequency (10 kHz) resistance. At 30 MHz the attenuation is high andrising rapidly to become and remain high through the microwave range.

The complete disclosure of the invention, which specifies the designcriteria for the secondary magnetic core half, is now presented withreference to FIGS. 13 and 13a.

FIG. 13 is an approximately to-scale drawing of a side viewcross-section of a preferred pot core configuration of the coilinvention, with a secondary center post 42 area. As approximately onehalf the primary center post 32 area Ap with typical approximatedimensions given in the table of FIG. 13a for the preferred applicationusing a 400 volt, 3 to 6 uF discharge capacitor (4). Preferred primaryturns Np is approximately 10 turns of approximately #10 Litz wire andturns ratio N is approximately 55 for a 33 kV peak output voltage Vs).Preferably, as per the parameters given in FIG. 13a, the secondarywinding is made up of an average of 22 turns (Nt) per layer andapproximately 25 layers N1 for low secondary winding 2 AC resistanceRsac and low output capacitance Cs, with the secondary wire comprisedpreferably of approximately #28 quad coated wire. Note that thedesignation "approximately" applied to a wire size shall be interpretedas the wire diameter of the specified wire size plus or minus 25% of thediameter, so that "approximately" #28 wire size (0.0125 OD copper) meansbetween #30 and #26 copper wire.

Typically, for the overall dimensions shown, winding width W1 isapproximately 0.3" to accommodate two layers of approximately No. 9 Litzwire, and W2 is approximately 0.6", i.e. W2 is about twice of W1.Winding length 12, shown as 0.9" in FIG. 13a, is varied from thatnominal value to accomodate more or less number of turns and/or largeror smaller diameter primary wire.

The design criteria for the secondary circuit (and entire coil) beginswith a derivation for the magnetic flux density Bs(t) in the secondarycore half of core cross-sectional area As. The derivation for specifyingthe magnetic flux density Bs(t) as a function of time is obtained bytaking the time integral of the integral form of Faraday's law andmaking Bs(t) the subject: ##EQU1## and using for Vs(t) the expressiondisclosed in U.S. Pat. No. 4,677,960 (as V2(t)) disclosed as part of thevoltage doubling principle:

    Vs(t)=[k*N*Vp/(1+(N**2)*Cs/Cp)]*[1-cos(Ws*t)]              [6]

Substituting and integrating, we obtain:

    Bs(t)=[k/UF]*[Vp/(2*pi*foc*Np*As)]*[x-sinx]                [7]

where

    x=Ws*t

    Ws=SQRT[UF/[Lpe*(N**2)*Cs]]

    Ws=2*pi*foc

    foc=fcc*SQRT[UF/(UF-1)]                                    [8]

    UF=1+(N**2)*Cs/Cp                                          [9]

where UF, the unity factor, is approximately (and greater than) equal toone, e.g. 1.1, for the present case wherein the Doubling principle isbeing used, and k is approximately (and less than) equal to one, e.g.0.95. The expression for Bs(t) can be easily referenced to Bmax whichhas to be initially evaluated in designing the coil, giving:

    Bs(t)=[k/UF]*[(fcc/foc)*(Ap/As)*Bmax]*[x-sinx]             [10]

    Bs(t)=Bs(t0)*[(1/pi)(x-sinx)]                              [11]

    Bs(t0)=pi*(k/UF)*(fcc/foc)*(Ap/As)*Bmax                    [12]

    Vs(t)=[k*N*Vp/UF]*[1-cosx]                                 [13]

    Vs(t0)=2*k*N*Vp/UF                                         [14]

where Ws*t0=pi, i.e. where t=t0 corresponds to half a wavelength of theopen circuit oscillation (and the time that Vs(t) takes on its maximumvalue).

For ease of discussion, there is assumed the typical values for thepresent application of this invention, k=0.95, UF=1.1, which givesapproximately:

    foc=3.3*fcc; [k/UF]=0.86

Substituting in the above, gives:

    Bs(t0)=pi*(0.86/3.3)*(Ap/As)*Bmax

    Bs(t0)=0.82*(Ap/As)*Bmax

    Vs(t0)=1.7*N*Vp

which now require interpretation, and will be given with reference toseveral cases of interest.

CASE 1: As a first case, the Voltage Doubling coil designed alongconventional lines wherein As=Ap is considered. In this case, the valueof the peak magnetic flux density Bs(t0) (at the time of peak outputvoltage Vs) is given by:

    Bs(t0)=0.82*Bmax

and for the preferred Doubling principle value of Vp=350 volts, N istaken in this example to equal to 50 to obtain:

    Vs(t0)=30 kV.

Inspection of the above reveals that with the standard types of coildesign used in conjunction with the Doubling principle, for the requiredpeak output voltage of approximately 30 kV the magnetic flux densityunder the open circuit conditions is somewhat less and about equal tothe value Bmax for the closed circuit or spark firing condition. Hence,for the case of ferrite core designs wherein the limitation is the coresaturation, there superficially appears to be little motivation for anew design.

For the present application we seek a high leakage inductance andcompact high efficiency coil design. High leakage inductance can beattained by a side-by-side winding. The area Ap is defined (limited) byBsat for ferrite cores, and by core losses for high Bsat materials (e.g.SiFe, NiFe, etc). If we could reduce the diameter or area As of thesecondary winding so that a wider, e.g. two-fold wider winding window 1swas provided for the wider space taken up by the secondary winding, thena very compact design can be achieved. But for area As not equal to areAp (based on the above values of k, UF), we have:

    Bs(t0)=0.82*(Ap/As)*Bmax

If we choose As to be approximately half the value of Ap for the typicalpreferred condition for a compact side-by-side winding with the sameoverall diameter D, as disclosed in FIGS. 4, 5, 6, 8, 13, and 14, thenBs(t0) becomes:

    Bs(t0)=1.64*Bmax

Hence, we see that for designs based on high Bsat materials, e.g. SiFe,NiFe, etc., where core loss is the predominant design criterion for highefficiency coils (based on the Voltage Doubling principle), and hencewherein the value of Bmax must be limited to less than half the value ofBsat, then the condition that Bs(t0) be less than Bsat is automaticallysatisfied, and the designs as presented with reference to FIGS. 5 and 6are complete and satisfactory.

CASE 2: A design for laminated 4 mil SiFe as per FIG. 5 is developedbelow:

Vp=350 volts

Cp=5 uF

Cs=180 pF

fcc=10 kHz;

foc=30 kHz, i.e. UF=1.1

Np=13;

We require that Vs(t0)=30 kV, and as per the Voltage Doubling principleof U.S. Pat. No. 4,677,960 as further specified in U.S. patentapplication Ser. No. 131,948 in an equation form for specifying N, andas further modified here to account for the fact that the couplingcoefficient k is not exactly 1.00 and UF is not exactly 1.00, we canobtain the turns ratio N for given values of Vs(t0) (simply designatedas Vs) for given values of Vp, Cs, Cp:

    N=[UF/k]*[Vs/2*Vp]*[1+(1/4)*(Cs/Cp)*(Vs/Vp)**2]

    N=[1.15]*[30,000/700]*[1.092]=1.15*47

    N=54

    Ns=700

and

UF=1.1 as assumed earlier

Ap=1 square inch

Bmax=0.62 Tesla

As=0.5 square inch

Bs(t0)=1.0 Tesla

and hence a satisfactory design is arrived at, recognizing that for theabove values of paramaters the core loss, which is based on Bmax and Vp(primary core volume), are comparable to the wire losses, assumingapproximately #9 primary Litz wire (with #27 to #33 wire strands) andapproximately #28 secondary single conductor wire (i.e. #30 to #26according to the definition of "approximately").

For the case of ferrite cores which have a lower value of Bsat, thedesign criteria are more complicated. Since core losses for the ferritematerial are a small fraction of the wire losses, optimal use the corematerial is achieved by preferably operating the core just below or atsaturation Bsat (or even somewhat above saturation), and preferablyusing a high Bsat material such as Ceramic Magnetics Mn67 or TDK H7c4. Avalue of 0.45 Tesla is assumed for such materials for the value of Bsat(for the typical operating temperature of 60 degrees C).

CASE 3: For performing the analysis, we assume the dimensions given inFIG. 13a, which represents a preferred design for a coil of 30 kVoutput, with fcc=10 kHz, Vp=350 volts, Np=11, and Ap=2 square inches togive a lower magnetic flux density.

As a sub-case, we take the above parameters to obtain:

Bmax=0.39 Tesla

Bs(t0)=0.64 Tesla

which we see is 0.2 Tesla above the Bsat so that the secondary core half(of area As=0.5 Ap) saturates prior to achieving the full output voltageof 30 kV.

It can be seen by reviewing the previous analysis that, just as theoutput capacitance Cs enters into the expression defining the VoltageDoubling principle (through UF), so it also (further) enters into theanalysis for the core saturation of the secondary core half throughBs(t). To reduce Bs(t) we need, among other things, to reduce Cs tobring UF closer to unity and hence make foc as large as practicalrelative to fcc while maintaining sufficient Cs to provide a substantialcapacitive spark.

CASE 4: As a general preferred case, it is proposed that Cs in units ofpF be numerically approximately twenty times equal to Cp expressed inunits of uF, i.e. we take the preferred values for the case of Vp=350volts:

Cp=6 uF

Cs=120 pF

which represents a 1/3 reduction in Cs over the previous case. We assumethe already specified value for k of 0.95, and for the remainingparameters the above values based on the primary circuit design, for nowleaving the remaining secondary circuit parameters (except Cs)unspecified:

Np=11 (#9 to #11 Litz wire)

Ap=2 square inches

which gives:

Bmax=0.39 Tesla

where the value of Np was selected to give a leakage inductance Lpe of40 uH, which for the capacitance Cp of 6 uF provides the preferredfrequency fcc of 10 kHz. Clearly, for a somewhat lower peak secondarycurrent (say 2.0 amps versus 2.5 amps) one can select Np=12 for Lpe of45 to 50 uH and Cp of 5 uF (to keep fcc equal to 10 kHz, which isexperimentally determined to give the SCR(s) sufficient time to recoverfor the operating condition of the ignition).

For the required 30 kV peak output voltage, we obtain for N:

    N=[UF/k]*[30,000/700]*[1+(1/4)*(120/6)*[(30/350)**2]

    N=[UF/k]*[43]*[1.04]=[UF/k]*45

    N=50 assuming UF=1.05 (which can be verified)

    Ns=550

    foc=4.6*fcc

which is 40% higher than the previous value. Substituting in theexpressions for Bs, we obtain:

    Bs(t0)=0.62*(Ap/As)*Bmax

For the otherwise same values (of the previous case) given in the tableof FIG. 13a, wherein Ap=2 square inches, As=1.1 square inches, we nowobtain:

Bs(t0)=0.62*1.8*Bmax

Bs(t0)=1.1 * Bmax=0.43 Tesla

which in this case is below Bsat for the core material, making for acomplete and satisfactory (consistent) design.

Note that the peak output voltage Vs can be increased to 33 kV byincreasing the secondary turns to 600 turns which is easily achieved bydesigning the secondary winding with, for example, 24 turns per layer(Nt) and 25 layers (Nl).

CASE 5: A practical case of a standard Ferroxcube core (part No.6656PLOO-3C8) is taken in which one core half behaves as the secondarycore half and the other core half has a ring placed on its center post(OD 1.11") to create a large diameter center post of 1.6". Recognizingthat the core is made of material 3C8 which has a Bsat of 0.40 Tesla(versus 0.45 Tesla for Mn67), a larger number of turns (Np=12 turns) isrequired in the primary winding. We further assume a value of Cp of 5 uFversus 6 uF to keep fcc at 10 kHz and to limit Bmax.

Below are given the various parameters:

Cp=5 uF

Cs=120 pF

Np=12

Ap=2.0 square inches

As=0.95 square inches

which gives:

Bmax=0.36 Tesla

N=[UF/k]*[43]*[1.045]=[UF/k]*45

N=50 assuming UF=1.06 (which can be verified)

Ns=600

foc=4.2*fcc

k/UF=0.9

Bs(t0)=0.67*(Ap/As)*Bmax=1.4*Bmax

Bs(t0)=0.50 Tesla

which is above Bsat of the 3C8 material (at 60 degrees C) by 25%.

This brings us to a further important feature of this invention whichallows us to correct the above problem of too high a value of Bs(t0) byother means than by increasing Bmax or the secondary core halfcross-sectional area As. This can be seen by writing the equations forVs(t) and Bs(t) in their time dependent form:

    Vs(t)=Vs(t0)*Fv[x(t)]                                      [15]

    Fv[x]=0.5*(1-cosx)                                         [16]

    Bs(t)=Bs(t0)*Fb[x(t)]                                      [17]

    Fb[x]=(1/pi)*(x-sinx)                                      [18]

    x=Ws*t

If we differentiate Fv and Fb (designated as Fv', Fb'), we obtain:

    Fv'[x]=0.5*sinx

    Fb'[x]=(1/pi)*(1-cosx)

Evaluated at the peak value for Vs, i.e. at time t=t0 (x=pi),

    Fv'[pi]=0

    Fb'[pi]=2/pi

and we see that, over the range of x between 0 and pi, Fv rises morerapidly than Fb. Initially, Fv rises slowly, then rapidly around x=pi/2,and slows up to a zero slope at its maximum value at x=pi; On the otherhand, Fb rises slowly, and gradually increases in slope to a maximumrate of rise at x=pi. More particularly, for x=x1=0.9*pi

Fv[x1]=0.975

Fb[x1]=0.80

so that if the turns ratio N is increased by 2.5% (and simultaneouslyfoc is kept constant, i.e. SQRT(Cs/Cp)/N is kept constant), then:

Vs[x1]=30 kV

Bs[x1]=0.40 Tesla

and full output voltage Vs of 30 kV is achieved even in this case byincreasing the turns ratio N by only a few percent.

Note that increasing the secondary turns Ns increases UF and hencereduces foc. More particularly, since foc is approximately inverselyproportional to the turns ratio N (and to the square root of the ratioCs/Cp), then one must approximately double the value of requiredincrease in turns ratio N (or reduce SQRT(Cs/Cp) proportional to theincrease in N. More exactly:

    Vs(t)=(N/NO)*Vs(t0)*Fv[x(t)]

    Bs(t)=(N/NO)*Bs(t0)*Fb[x(t)]

where N is the value we have increased NO to in order to reduce Bs(t).

While we are free to choose x1 (and hence the new turns ratio N), thevalue X1=0.85*pi is selected as a good design value.

Fv[x1]=0.95

Fb[x1]=0.70

Increasing the turns ratio by 5% i.e.

    N/NO=1.05

    Vs[x1]=1.05*0.95*Vs(t0)=Vs(t0)

    Fb[x1]=1.05*0.70*Bs(t0)=0.75*Bs(t0)

so that we can achieve an approximately 25% reduction in As if we selectthe turns ratio N so that it provides a peak output voltage Vs which is5% above the design value Vs(t0) (assuming the secondary core does notsaturate even though in reality it would).

This is an important result in that it gives additional flexibility indesigning the coil of the present invention. More particularly, itsuggests designing the primary core area Ap and primary winding Np forappropriate Bmax, e.g. to have Bmax approximately equal to Bsat, andsuggests designing the secondary core area and winding to make use ofthe above phenomenon of the differing slopes of Fv and Fb, andparticularly to select the turns ratio N to be 5% greater than itsdesign peak value Vs(t0) so that As can be reduced by approximately 25%.

CASE 6: Another embodiment of the invention is one in which the smallsize of the coil and the design principles presented herein areadvantageously made use of to develop a coil design suitable for adistributorless ignition. Preferably, a higher frequency of oscillationfcc is used, e.g. 20 kHz, achieved by using a faster turn-off SCR, orallowing the SCR to ring, etc. Ferrite core material is used because ofthe high frequency of 20 kHz. This higher frequency is preferablyattained as follows: Ap=1 square inch

Np=11

Cp=3 uF, Lpe=20 uH

fcc=20 kHz

and by careful design we can also achieve:

Cs=60 pF (40 pF in coil, 20 pF in plug)

N0=50

UF=1.05

foc=4.6 fcc

Vs(t0)=30 kV

In this way, the coil size can be reduced to approximately half the sizeof the coils disclosed, and by using a 5% higher turns ratio N (53instead of 50) than predicted based on the time x(t0), one can furtherreduce the secondary cross-sectional area As than otherwise expected (by25%).

    As=0.42 square inches (diameter of 0.65")

    Bmax=0.39 Tesla

    Bs(x1)=0.61*0.75*(Ap/As)*Bmax

    Bs(x1)=0.42 Tesla

With reference to FIGS. 13, 13a, the same length dimensions 11, 12, 13,14, are preferably used with the revised cross-sectional dimensions:

D=2.0"

a1=1.65, a2=1.15, W1=0.25

a3=1.75, a4=0.65, W2=0.55

and we see that appropriate dimensions are produced, especially for thewinding window W2 which is maintained at a large value of approximately0.55 inches.

Note that the above design can be implemented in the coil depicted inFIGS. 7 and 7a. Also, such a design may be particularly useful where alarge amount of energy is required to be delivered rapidly, as in acavity type plug of a plasma jet type of ignition. In this case evenhigher frequencies can be used, e.g. 30 to 40 kHz, for further sizereduction and lower number of turns of primary and secondary wire.Semi-standard ferrite "E" type may easily avail themselves to thisapplication wherein the area As of the center core of the secondarysection is made about half that of the primary area Ap.

An alternative way to operate the ignition in general, and in particularto achieve a small coil design for a distributorless (or otherapplication) ignition while retaining the features of the MPCDRC design(using existing high efficiency slower turn-off SCRs with fccapproximately 10 kHz) is to use other than 400 volt rated capacitors asalready disclosed. Use of lower capacitance Cp, 600 volt capacitorswould lead to a higher primary turns Np (higher leakage inductance Lpe)and more efficient operation of the SCR. Use of a higher capacitance Cp,250 volt capacitors would lead to lower primary turns Np. In both casesthe secondary turns Ns would be approximately unchanged. Each approachhas its respective advantage which must be studied case by case based onthe principles presented here.

It should be noted that in all the cases 1 through 6 above, a typicalprimary resistance Rp is approximately 5 milliohms and the typical DCresistance of the secondary winding is between 10 and 20 ohms(equivalent primary resistance of 4 to 8 milliohms for turns ratio N of50). The AC resistance of the primary winding assuming Litz wire isapproximately the same as the DC resistance, while the AC secondaryresistance can be kept below about twice the DC resistance byappropriate design, as already disclosed. Thus, a total primary ACequivalent resistance of 12 milliohms is attainable with this design,representing a very low AC resistance not achieved by any known designsprior to the present ones.

It is noted with reference to the tables of FIGS. 5a, 7a, and 13a thatthe cross-sectional area represented by the outer post 65 is typically10% smaller than the area of the center post 32c. This feature wasexperimentally discovered and is incorporated in the design of the core.

FIG. 14 is a half side view cross-section of a preferred embodiment ofthe coil invention showing an alternative means of constructing thepreferred core embodiment. The main feature represented by FIG. 14 is ameans to construct out of one piece 64 and a cap 68 a single core 64(pot type core shown here) with the two differing center post diameters(area Ap of post 32c and area As of post 42c, as in FIG. 7) andconnected outer core sections 65 and 66. The structure is convenient fora pot core design since height W2 is larger than W1 and a mold is easilyconstructed to produce the shape 64 shown, while cylindrical cap 68 issimple to fabricate. Similarly, one can design a laminated E corewherein cap section 68 can be obtained in two equal section lengths 1cfrom an inner section of length 1c by removal of the winding windowsections W1 and W2 in two steps wherein length 1c and width W1 is firstremoved and section of width W2 is removed as a second operation tominimize waste of the lamination material.

In this drawing is also shown a preferred secondary winding 62 which hasan initially variable turns per layer (Nti per ith layer) so that thelower voltage layers 62a can contain more turns per layer since theyneed only a small clearance 62c to ground, and the higher voltage layers62b contain fewer turns per layer. For example, one can have thefollowing sequence of turns per layer, Nt1=36, Nt2=35, Nt3=34, . . . ,Nt16=21, Nt17=20, Nt18=20, and the remaining layers having twenty turnsper layer.

While the design principles presented herein are applicable to pot coresand "E" cores, they can also be applied in other types of cores asbriefly presented next.

FIG. 15 is a variant of a standard form of high leakage inductance coilwinding modified to more optimally use the design criteria of thepresent invention. The main feature here is to recognize that thewinding 71 on the primary winding post 73 of area Ap produces the majorpart of the leakage inductance, and the winding on the secondary windingpost 74 of area As the minor leakage, and hence As can be made, say,half of Ap as per the principles presented herein, as long as in thisparticular case the secondary winding produces less than half theleakage magnetic flux density and leakage inductance Lpe. Note that inthe prior cases practically all the leakage inductance is produced bythe primary winding. The area Aps will be between Ap and As and can beexperimentally determined.

The invention as presented herein has certain further useful aspects,some of which were discovered as the very consequence of using thefeatures of the invention.

For example, when using the invention in a MPCDRC ignition with apreferably high efficiency high output power converter of the typedisclosed in patent application Ser. No. 179,953, one is able to firemany pulses, e.g. 10 to 20 pulses per ignition firing, and one is ableto keep the initial primary voltage Vp of 350 volts from falling below200 volts. When doing this in conjunction with a spark plug with atoroidal gap, one notes the tendency of the multiple spark pulses tomove along the periphery of the toroidal gap to a greater or lesserextent depending on the time between pulses. For example, for a periodof 100 usec between pulses (defined as Toff, equal to (Ti-Te) withreference to FIG. 2a), the spark pulses tend to cluster in one region,while for a period Toff of 400 usec they tend to spread uniformly aroundthe periphery of the gap. Moreover, the sparking sound at the higherToff time is more of a crackle (with higher breakdown voltages of thesubsequent pulses) indicating that the spark plasma has more fullyrecovered (towards an insulating dielectric) between pulses.

This phenomenon has several consequences. First, it indicates a naturaltendency for the spark remnant (fully discussed in patent applicationSer. No. 131,948) to reside on the outer surface of the spark dischargeversus in the center of the discharge (as indicated by the tendency ofthe pulses to move sideways along the toroidal gap). This phenomenonwill be further enhanced in the flame environment where chemi-ionizationwill increase the electrical conductivity at the surface of thedischarge (location of the flame front or reaction zone). Hence, thephenomenon of Pulsed Flame Discharge Ignition (PFDI) first disclosed inpatent application Ser. No. 131,948 will only be further enhanced by theability to utilize more pulses per firing and to modulate the pulsetrain firing frequency as disclosed.

Secondly, this phenomenon gives further credence to the model for thedecay of the spark discharge and growth of the flame front dischargewith time constants of 50 usec (and density scale of 10**11electrons/cc) as per the PFDI model. More recent evidence indicates atime scale of 100 usec as the appropriate time scale (and a somewhathigher density scale).

In patent application Ser. No. 131,948, in-cylinder air-motion, type offuel, plug tip geometry, etc, are shown to play a role in the formationof a large flame kernel as a result of the PFDI phenomenon. The presentinvention, in the form of a MPCDRC ignition with many pulses at a highenergy, e.g. later pulses having about the same energy as the initialpulses, will allow for more effective design of the overall ignitionoperation to improve initial flame growth. For example, it has beenexperimentally observed that with a long pulse train where the time Toffis gradually increased (modulated) between 200 usec and 400 usec, thevoltage Vp, which initially drops slowly to say 250 volts (from a highof 350 volts) will recover and at the later, e.g. tenth pulse, be backup to 350 volts to further increase the size of the initial flamekernel.

These features, e.g. PFDI effect, are more optimally utilized by meansof a plug of the EFFL type mentioned above and further detailed belowfor the present application.

FIG. 16 is a cross-sectional view of a preferred embodiment of atoroidal gap EFFL type spark plug suitable for use with the present coilinvention, and particularly used as part of an MPCD ignition system withmany pulses per spark firing. Such a plug has been disclosed in U.S.patent application Ser. No. 131,948, with this version beingparticularly well suited for the present coil application. The plug isshown approximately twice scale and is based on a standard design havinga 14 mm thread 84a whose length (reach) is approximately 3/4 inch.

Center conductor section 91 of diameter t2 is preferably in between 0.1and 0.125 inches so that with tight fitting insulator 87 of thickness t1of approximately 0.12 inches and conductor 84 a significant capacitanceof 10 to 20 pF is provided. Center conductor section 90 of thickness t4of approximately 1/4 inch provides a capacitance of 15 to 30 pF withinsulator layer 88 of thickness t3 (of approximately 0.11 inch) andtight fitting outer metallic layer 89 contained in (or part of) metallicshell 85. Shell 85 is preferably of length Lshell between 1 and 1.5inches to provide, with capacitance along plug threaded portion, a totalmoderate value of plug capacitance of approximately 40 pF (for aluminainsulator) to provide minimally sufficient capacitive spark withoutunduly loading, i.e. lowering the open circuit peak voltage Vs. Sparkplug insulator 88/87 is preferably high purity alumina (95%+) ofapproximate thickness shown to provide the moderate value of required 40pF capacitance. Use of higher dielectric constant material, e.g.dielectric constant of about 30 (versus 9 for alumina) will allow for adesign of a plug similar to standard plugs in so far as overall lengthis concerned since the capacitance of standard plugs is typically 10 to15 pF.

Spark gap 17a is preferably approximately 0.1 inches for engineapplications of moderate, e.g. 8.5:1, compression ratio. Material oferosion resistant plug tip 82 and annulus 81 are preferably ofTungsten-Nickel-Iron, Tungsten-Nickel-Copper, or other erosion resistantmaterial to withstand the higher peak current of about two amps and thelarger number of pulses per ignition firing made possible by theimproved ignition system. Spark plug tip 83 may be present for near TDC(Top-dead-center) engine firing to the piston (or rotor, or othercompression means) as disclosed in U.S. Pat. No. 4,774,914, whereinthere is also disclosed a preferred ignition firing envelope with a peakbreakdown voltage of, say, 30 kV and a minimum breakdown voltage of,say, 8 kV.

With reference to FIG. 16a, there is depicted a fragmentary partial viewof the plug tip defining angles theta1 of preferably 0 to 30 degrees,theta2 of 60 to 90 degrees, theta3 of 0 to 30 degrees, and theta4 ofapproximately 45 degrees to define a concave insulator surface 86a/86b.The center electrode button 82 is of thickness t5 approximately 1/16inch to help concentrate the electric field at its edge to reduce thebreakdown voltage (from excessively high values). Length Lgap, asalready stated, is preferably 0.1 inch for typical gasoline engineapplications.

A preferred embodiment of the plug tip of FIG. 16a is shown in FIG. 16b.End button 82 has the following approximate values for the anglesdefined:

theta1=0 degrees

theta2=60 degrees

theta3=18 degrees

theat4=48 degrees

The angle the spark makes with the vertical, theta5, is preferablyapproximately 45 degrees as shown. This is achieved by using a diameterof button 82 of approximately 0.28 inch and an annulus 81 which isrecessed and defines a diameter of 0.38 inch versus 0.35" defined by thediameter made up of the sum of the thicknesses t2 plus 2*t1. Note thatbutton 82 of FIG. 16 is similar to that of FIG. 16b except angle theta2is 90 degrees in the case of FIG. 16 to make for a simpler design. Fromdimensional considerations, length of surfaces 86a and 86b areapproximately 0.08 inches for the typical gasoline engine applications.Clearly, where it is practical, these dimensions will be larger, e.g.1/8" to provide a larger gap Lgap of greater than 1/8". For example, inlow compression ratio e.g. 7 to 1, two stroke engines, or cases wherepiston firing at TDC is possible, larger gaps Lgap are possible.

There are numerous special applications of the coil invention,especially when it is used with an MPCDRC ignition circuit. For example,in the case of engines using alcohol fuels, e.g. methanol, ethanol,etc., the ability to deliver hundreds of watts of ignition power overseveral milliseconds to deliver hundreds of millijoules of energy to theair-fuel mixture, especially under cold start conditions, could allowalcohol fueled cars to start at very low temperatures without otherassistance and to operate as successful lean burn vehicles. Moreover, itis a simple matter to use the above-described structure to extend theduration of the non-decaying or very slowly decaying (or first decayingand then growing) pulses during the engine cranking stage by means ofthe ignition controller so that, say, about twice the normal energy(compared to idle engine operation) is delivered to the air-fuelmixture.

Besides ignition applications, the present coil, i.e. transformerinvention, lends itself to other applications where high leakageinductance is required (achieved through a side-by-side winding). Forexample, the power converter of U.S. Pat. No. 4,868,730, which operatesinto a capacitive load which is charged to about half the maximum valueas dictated by the transformer turns ratio, could be more optimallydesigned by having a somewhat smaller secondary winding core center postto provide a larger secondary winding window (and preferably widerwindow to provide more turns parallel to the leakage magnetic flux linesas already disclosed for low AC resistance) and/or to accomodate Litzwire which may be required at the preferred higher frequency ofoperation of 40 kHz to 100 kHz.

The side-by-side feature of this invention lends itself to furtherimprovements and flexibility of design of both the coil and of theentire ignition system. In particular, as depicted in the preferredembodiments of FIGS. 17 to 21, the coil makes for very low cost,compact, and more universally applicable ignition systems, particular inthe form of at least two types of pure distributorless ignition systems.

It is particularly worth noting that with reference to FIGS. 4, 5, 8,and 13, each half core 31 and 41 can be made of different magneticmaterials. In FIG. 17 is depicted a low loss, preferably ferrite,magnetic material core half 31 in which the primary wire 1 is wound, anda low cost (higher loss) high magnetic saturation material, such asSilicon Iron (SiFe), core half 41 on which the secondary winding 2 iswound.

In a preferred embodiment (of FIG. 17), the secondary core half 41 canbe made of low cost 7 mil (0.007 inch) laminations to the dimensions ofa Single Phase-5/8 LSW EI lamination, as per the Thomas and Skinnerhandbook, excepting that the length of the leg 14 is preferably shorter,e.g. 1 inch. The primary core half 31 can be made of the ferrite potcore design given in "Case 5", of approximately 25/8 diameter (as in the5/9 LSW EI lamination, i.e. D=25/8) with a ferrite ring 32dd added tothe center leg 32d to provide an approximately 1.55" center postdiameter, and a disc 32de added. In this way, for a primary number ofturns Np of 12 and for the remaining parameters assumed from the exampleof "Case 5", the secondary core half 41 is stressed to approximately 1.0Tesla and the primary core half is stressed to approximately 0.3 Teslafor an suitable design for the maximum stressed open circuit voltagecondition of 30 kV. During the spark firing condition, the magnetic fluxis carried principally by the low loss primary core 31 versus by thehigh loss laminated core half 41, making for a more optimal use of thecharacteristics of the two materials used.

In this regard, one can view this use of disimilar magnetic materials asa more optimal design in that one is using each material to advantage.One uses the much higher saturation flux density of SiFe to reduce thecenter post (42) area As of the secondary core 41 to approximately 1/2square inch for approximately half the length of secondary winding wireand better than half the resistive losses (when one factors in the ACloss effect). This material's higher losses are acceptable because ofthe very short duration of the open circuit high voltage condition, i.e.the core is subject to a high magnetic flux (above 0.25 Tesla) only forthe first few usecs of the first spark pulse of the multi pulse ignitiontrain. For example, using the more optimal newer developed 7 millaminations (which cost only 50% higher than 14 mil lamination) one hasthe highest possible losses of a few kilowatts at the peak flux densityof 1 Tesla and for a maximum rise time of a few microseconds for a totalenergy loss of about 5 to 20 millijoules. This is acceptable given thetypical total energy dissipation in the first pulse is about 30millijoules. During the spark firing condition the magnetic flux iscarried mainly by the primary low loss ferrite core 31 so the secondarycore high losses do not compromise the design.

By comparison, in the typical preferred embodiments of two ferrite potcore halves, the secondary pot core half 41 is stressed far less duringthe spark firing condition (and hence under-utilized in this condition)since most of the (uncancelled) magnetic flux 30 is contained in theprimary core half 31, and hence the properties of the secondary corehalf 41 are not fully used.

FIG. 17a is a preferred embodiment of a coil sized similarly to that ofFIG. 17 with preferred approximate dimensions shown for the presentapplication, and wherein the primary winding 1 is split into twowindings, one winding 101 contained in the laminated section 41a (withan isolating standard lamination 94 which is part of a no wastelamination construction), the other winding 110 contained in the primarycore half 31a now representing an actual separate choke uncoupled fromthe secondary winding 2a. Winding 101 contained in (compact coil)structure 41a comprises a very low leakage inductance primary winding ofa compact transformer or coil with very low winding losses. Each part(41a and 31a) represents a stand alone device having respective cap ends94 and 94a. As a single unit they can, for example, share, the laminatedcap 94 between them.

In the preferred embodiment shown the coil has approximately 8 primarywinding turns Np1, i.e. 6 to 10 turns, and approximately 400 secondaryturns Ns, i.e. turns ratio N of 50 for the present application alreadydisclosed, and a very low leakage inductance Lpel (which typicallymeasures at about 2 uH). Smaller gauge litz wire is used for the primarywinding, e.g. approximately No. 12 Litz wire with 30 to 33 gaugestranded wire, and preferably 27 to 31 gauge magnet wire for thesecondary winding 2a. The primary core 31a, of approximate dimensionsshown, has preferably approximately 12 turns of (approximately No. 10Litz) wire Np2, and an air-gap 38a for adjusting the leakage inductanceLpe2, which is equal to approximately the total inductance Lpe in thiscase, say approximately 50 uH for the discharge capacitor value Cp of 5uF. In operation the configuration of FIG. 17a does not differ from thatof FIG. 17, excepting for the differing number of turns Np1 and Np2(Np1=Np2 normally), and the advantages which may accrue due to theseparation of the two functions, the transformer function and theleakage inductance function.

By decoupling part of the primary winding from the secondary winding,the AC losses of the secondary winding are reduced due to a lowerprimary winding leakage flux cutting the secondary winding turns. Hence,relatively heavier secondary winding wire can be used. It also reducesthe overall transformer core losses by weighing the total core losses inproportion to the leakage inductance of each part, so that the lowerloss separate leakage choke 31a has a much higher weighting factor (bydesigning Lpe2 to be much greater than Lpe1). In this way lower cost,higher magnetic saturation, higher loss material, e.g. SiFe, can be usedfor the first transformer part to reduce overall cost and losses.

An alternative form of design is to wind the coil part 41a as aside-by-side winding which may provide, for example, 10 uH of leakageinductance. In this way, the required leakage (choke) inductance of theprimary part 31a can be reduced to, say, 40 uH for a total 50 uH leakageinductance. This would allow the number of turns of the choke winding110 to be reduced by 20%, from, say, 12 turns to 10 turns. During sparkfiring the core of coil 41a would thus carry 20% of the total magneticflux which would be acceptable for a higher loss material and would makefor a better overall balance of magnetic stress (flux density betweenthe two parts).

The main advantage of this design is that simple and low cost forms ofdistributorless ignition now become possible by allowing the singleleakage choke Lpe2 to be shared between several transformer coils 41a(with very low leakages Lpe1) which can be made very small and cheapthrough the use of SiFe laminated magnetic core material.

FIG. 18 depicts a preferred embodiment of such distributorless ignitionsystem in circuit diagram form based on the conventional CD circuittopology disclosed herein. It shows two compact coils 103a, 103b, itbeing understood that more can be added by cascading from points 112 and110a. A single leakage inductor designated as 110 is shown which isshared by the compact coils 103a, 103b.

In this embodiment, each compact coil 103a, 103b, . . . , has genericprimary winding 101, secondary winding 102, high voltage terminal 107,associated discharge capacitors 104a, 104b, isolating diodes 108a and108b, and SCRs with return diodes 105a/106a and 105b/106b. Such compactcoils are preferably of the type 41a, and leakage inductor chokepreferably of the type 31a, both shown in FIG. 17a. The two (or more)coil circuits are tied together at terminal 109 which is preferablyconnected to recharge circuit choke 9 (as already disclosed).

In operation, when gate of SCR 105a is triggered, negative voltage VP(preferably approximately 350 volts) appears almost totally acrossprimary winding 101 of respective coil 103a since its primary (ormagnetizing) inductance Lp1 is generally at least one order of magnitudegreater than the choke inductance Lpe, e.g. about 1 mH for Lp versus 50uH for Lpe. Upon spark formation by secondary winding 102 (of coil103a), inductance presented by the primary winding 101 drops to theprimary leakage inductance Lpel, which is much less than chokeinductance 110 (Lpe), and node point 110a oscillates with approximatevoltage-Vp*cos(wt). Hence, the non-firing circuit (of coil 103b) isinactive, excepting that the voltage seen by the SCR/diode pair105b/106b may be up to close to double that otherwise seen.

FIG. 19 depicts an alternative form, i.e. topology, of spark ignitioncapacitive discharge circuit which is particularly well suited fordistributorless type ignition systems. This preferred embodiment is madepossible as a result of the presence of the isolation choke 9 of therecharge circuit comprising capacitor 10, choke 9, and diode 8. In thistopology, designated as ACD, the discharge capacitor 104 is connectedbetween the output of the recharge circuit, node 109, and ground, andnot in series with the transformer primary winding 1. SCR 105 and diode106 are connected, as shown, between the low side of primary winding 1and ground. Capacitor 4a and resistor 4b constitute a snubber pair,wherein capacitor 4a can have a value as small as about 0.01 uF for thecase where a preferred SCR is used which has a high rate of rise ofrecovery voltage, such as a TAG S4014MH SCR.

In this ACD topology, when SCR 105 is triggered node point 109 isbrought to ground and a positive voltage Vp appears across primarywinding 1 to create a high voltage across the secondary winding 2 tobreak down a spark gap. The spark current oscillates between the seriescombination of capacitor 104 and primary winding 1 through SCR 105 inthe first half cycle, and through the shunt diode 106 in the second halfcycle. In the second half cycle a second path is possible, permittingcapacitor 104 to discharge through diode 8. But since recharge circuitchoke 9 is present, and since its typical inductance is over a hundredtimes greater than Lpe, i.e. about 20 mH versus about 50 uH for Lpe, thesecond path is in effect blocked due to its two orders of magnitude orgreater impedance. In this way, the topology of FIG. 19 is analternatively equally valid capacitive discharge circuit for the case inwhich the recharge circuit (with choke 9) is used.

FIG. 19a is a preferred embodiment of the alternative capacitivedischarge circuit (ACD circuit) in which a separate external choke 110is placed in the preferred position shown, i.e. between capacitor 104and ground. In operation it is the same as that of FIG. 19, exceptingthat whereas node 109 of FIG. 19 oscillates as Vp*cos(wt) during asparking discharge cycle, node 111 oscillates as -Vp*cos(wt), assuminginductance of inductor 110 (Lpe2) is much greater than leakageinductance Lpe1, e.g. 50 uH versus 2 uH. Hence, node 111 is suitable forproviding a negative bias to gate 5a of SCR 105 during spark dischargeto speed up the turn-off of SCR 105. Fast turn-off circuit compriseshigh voltage diode 113, resistor 114 (typically a one to two wattresistor of value 1 kilohm to 5 Kilohm), capacitor 115 of value about0.1 uH, and gate resistor 116 of typical value 100 to 500 ohm. Suchspeed-up turn-off has been disclosed in U.S. Pat. No. 4,841,925.

FIG. 20 is a circuit diagram of the preferred distributorless ignitionsystem based on the ACD topology in which one discharge capacitor 104and one external leakage inductor 110 serve several (N number) compactignition coils T1 (103a), T2 (103b), . . . Ti, . . . TN. In thispreferred embodiment, cascaded circuit sections comprising the seriescombination of the primary winding of the compact coils T1, T2, . . . ,Ti, with their respective SCRs (shunted by a diode) are each in serieswith the capacitor 104 and choke 110 to form a complete ignition firingcircuit. That is, primary winding of coil 103a with its SCR and shuntdiode (combination 105a/106a) comprise a series section also in serieswith capacitor 104 and choke 110, as does primary winding of coil 103band the SCR/shunt diode combination 105b/106b (the switch), and so onfor additional coil/switch series combinations cascaded from point 112as shown.

In operation, when SCR 105a is triggered, as in the case of FIG. 19a,voltage Vp appears across primary winding of coil T1 to fire its sparkgap. Upon firing of T1, node 109 is at a voltage whose maximum valueequals (Lpe1/Lpe)*Vp, which is typically well below 1/20 of Vp, or below20 volts, i.e. Lpe1 is typically about 2 uH and Lpe is typically about50 uH. Hence, coils T2, T3, . . . , cannot fire their respective sparkgaps since at most they can see 20 volts across their primary windings,which is not sufficient to fire their respective spark gaps even at thelow pressure conditions of cylinders of multi-cylinder engines, whichmay, for example, be near the bottom of the intake stroke during firingof a cylinder under compression.

During the second half discharge cycle all the shunt diodes 106a, 106b,. . . , represent possible paths for the return current. However, sinceall but the primary winding of the fired coil T1 present theirmagnetizing or primary inductance Lp which are much greater (100 to 1000times greater) than the leakage inductance presented by the fired coil(T1), then essentially all the current returns through the shunt diode106a of the triggered SCR. In this way, each compact coil (withpreferably concentric, very low leakage inductance windings of typically1 to 2 uH) can be fired independent of the others, and a low cost,simple form of distributorless ignition system is attained.

In this preferred embodiment speed-up turn-off circuit made of likecomponents as in FIG. 19a (components 113, 114, 115, 116) requires anadditional diode for each additional transformer to isolate each gatefrom the other, diode 117a for gate 105a, diode 117b for gate 105b, andothers as required connected to node 118.

While not explicitely shown, it is clear that in distributorlessignitions one needs sensors to trigger each SCR of each coil at itsappropriate time in the engine cycle. As a retrofit kit for ignitionscurrently having a distributor, the high voltage terminals of thedistributor can, for example, be grounded through say 100 ohm resistors,and the distributor used as a dummy firing distributor to fire each coilat its appropriate time.

While the parallel, part circuits, of the series combinations of coilsT1, T2, . . . , Ti, and switches S1, S2, . . . , Si, cannot be firedsimultaneously (unless leakage inductor 110 is eliminated and built intoeach transformer Ti), effective simultaneous firing of, say, two coils(T1 and T2) can be achieved by alternatively triggering their respectiveSCRs from a pulse train with firing to non-firing duty cycle of lessthan 50% each. Alternatively, a second bank of coils, switches, etc.,can be connected to node point 119 through a second isolating diodesimilar to diode 8 to thus have a second independent set of coils withtheir own leakage coil and discharge capacitor. Such an embodiment wouldbe particularly well suited in the case of rotary engines and certaintwo stroke engines which use two plugs per rotor. For a three rotorengine, one would require two sets (connected to node point 119) ofthree coils T1, T2, T3, and T1', T2', T3', each set having one dischargecapacitor (104, 104') and leakage choke (110, 110'), and all the unitsbeing driven by one high power, high efficiency, power converter and onerecharge circuit. Alternatively, one can further reduce the system partscount by having only one set of six coils with only one dischargecapacitor 104 and leakage inductor 110 and fire the coils in pairs onalternative pulses of an otherwise two-fold longer duration sparkpulsing train of less than 50% duty cycle.

FIG. 21 is an approximately half scale schematic of an actualdistributorless ignition of FIG. 20 for a four cylinder engine. In thispreferred embodiment, compact coils T1, T2, T3, T4 and choke 110 are ofsimilar design as transformer (coil type) 41a and leakage choke 31arespectively of FIG. 17a. Capacitors 104 (one or more in parallelcapacitors) are preferably located at the site (two shown) of leakageinductor 110, as are the speed-up turn-off circuit comprising parts 113,114, 115, and 116 (see FIG. 20).

In this one of many possible parts configuration the coils T1 to T4 andchoke 110 are shown in line with the coil high voltage towers 48a, 48b,48c, 48d located on the side and above the winding (101/2a as per FIG.17a). Each switch S1 through S4, which is preferably an SCR with builtin diode, is shown located at the site of each respective coil andmounted on a grounded case 120.

Another configuration for the coils and choke is an essentially circularone in which choke 110 and capacitor 104 are located at the center andthe coils on a perimeter around parts 104/110.

Another configuration is one in which switches S1 through S4 aredirectly mounted (without insulation) to a grounded heat sink 120, i.e.with the SCR anode tab directly mounted to 120. This is accomplished byhaving the power converter voltage Vc (FIG. 20) be of negative polarity,and the SCRs and the diodes comprising switches S1 through S4 reversedin direction from that shown in FIG. 20. The gates of the SCRs must thenbe isolated. Also, in this configuration (with reference to FIG. 20)leakage choke 110 would be preferably located on the high voltage sideof discharge capacitor 104 defining a new node point 111' between them(not shown) and the cathode of diode 113 connected to the point 111'.

FIG. 22 is an approximately half scale schematic of a very small compactcoil Ti (as in a distributorless ignition of FIG. 20 showing multiplecompact coils T1, T2, . . .) wherein the coil core material is made of aformed, i.e. pressed or molded, material of inherently high saturationflux density, or of a material which in molded form exhibits the abilityto sustain a high impressed magnetic field. The coil core material canbe made of low cost moderate loss Powdered Iron or Silectron, Hi-Fluxpowder material (an Arnold Nickel-Iron material), or any of a variety ofhigh saturation flux density materials. Preferably, the shape of thecore (and hence coil) is an elongated pot core structure 41b with a cap94 and cylindrical center post 42d of preferably approximately 5/8 inchdiameter for the present application. Preferably primary and secondarywindings 101 and 102 are side-by-side windings of, say, approximatelyeight turns of primary wire and 440 turns of secondary wire for asomewhat higher turns ratio N of 55. This elongated design shown issuitable for mounting over a spark plug 16 to provide a particularlycompact overall design, with the two layered primary turns 101 locatedat the opposite end from the high voltage terminal of the spark plug 16for easy connection of wire 101 to a switch S and to a leakage chokeinductor Lpe and a discharge capacitor Cp. In this design, cylinder head17 preferably has a well for supporting the entire compact coilstructure. The high voltage lead 48e is preferably contained in anelastic (silicone) material 121 comprising special spark plug boot whichis mounted over the spark plug and connected via a terminal 122.

It should be appreciated that other useful configurations of a (lowleakage inductance) compact coil are possible once the separation of theoverall coil structure has been made into a high leakage choke part 110and a compact transformer coil part Ti. In addition, it should beappreciated that the alternative topology of capacitive dischargecircuit of FIG. 19 (designated as ACD) made possible by the use of theisolation choke 9 of the recharge circuit 14 (FIG. 1) is more usefulthan the basic CD circuit (designated as BCD when needing to distinguishit from the ACD circuit) in using the compact coil for distributorlessignition.

In FIG. 21 was shown a schematic of a side view of a possible layout ofthe coil assembly, as it shall also be referred to hereinafter, of thedistributorless ignition. In FIG. 23 is shown an approximately fullscale drawing of a top view of a preferred embodiment of the coilassembly for a four cylinder engine. The drawing is in part fragmentaryin that only one of the switches S1 is shown in detail, as is the casefor compact coil T1.

In this preferred embodiment of FIG. 23, the compact coils T1, T2, T3,T4 are placed at the corners of a rectangular plate 120, with the coilhigh voltage towers 128a, 128b, 128c, 128d preferably placed on theoutside of the plate as depicted. The leakage inductor 110, orresonating inductor, is placed between a pair of the compact coils,between T1 and T3 in this case, with the discharge capacitor means 104placed either on top of inductor 110 as shown, or alongside inductor 110between coils T2 and T4 as indicated in the embodiment of FIG. 26.

In the present case, one end of the inductor winding (110a of FIG. 23b),designated as 110aa, is conveniently connected to one end of capacitormeans 104 via strap 111. The other end of the inductor winding, 110ab,is connected to a ground plane 125 which is preferably placed on theplate 120. In this configuration, the SCR/diode pairs S1, S2, S3, S4,are preferably mounted on the plate 120 as shown, which acts as anexcellent heat sink for the devices and also allows for convenientplacement of the terminals of the devices onto a single ground pad 125and to each of four respective high voltage pads (pad 126 shown for SCR105a and diode 106a). The high voltage pads are in turn used to makerespective connections to a primary winding end of each coil (connectionto end 112a of primary winding 101 of coil T1 shown in the drawing). Theother ends of the four primary windings of the coils T1, T2, T3, T4, areconnected to pad 124 which is connected to capacitor means 104 and tofeed voltage terminal 109.

In this preferred embodiment only one snubber is used, which iscomprised of capacitor 4a and resistor 4b, connected between the highvoltage strap 124 and ground. The snubber action is not as effective ashaving a snubber for each semiconductor pair S1 through S4, but isadequate for proper operation of the discharge circuit. Also shown arethe fast turnoff circuit comprised of the diode 114, resistor 114,resistor 116, and capacitor 115, as per FIG. 20. The compact coilsshown, T1 through T4, are a preferred embodiment of the coil shown inFIG. 23a. In these drawings, the coils have a square center leg 132 anda window 133. Fasteners for mounting the plate can be convenientlyplaced as shown in locations 131 and 131a, consistent with theorientation of the coils.

FIG. 23a depicts a full scale drawing of a side view of a preferredcompact coil on the form of laminations, preferably the relatively newlow cost, low loss 7 mil laminations. In this design, a winding window133 of width 0.5 inch is shown to be sufficient for accommodating theprimary winding 102 and secondary winding 2a, based on the primarywinding 101 comprised of rectangular copper strip of approximately 0.1"wide by 0.040" thick. The thickness is approximately equal to andgreater than the skin depth at the preferred operating dischargefrequency of 10 KHz to give an AC resistance no higher than 50% of theDC resistance. Eleven turns of primary winding are shown here andapproximately 600 turns of secondary winding of approximately 30 gaugewire.

A consideration in arriving at this design is to provide a higherprimary inductance at the open circuit operating frequency ofapproximately 30 KHz. Laminated material has a decreasing effectivepermeability with frequency, and given it is desired to have an opencircuit inductance Lp1 at least three or four times greater than theleakage inductance Lpe (for 75% to 80% available voltage Vp to thecompact coils), then preferably magnetic path length "1" should be assmall as practical.

In this design, a preferred overall dimension is D=21/2" by L=21/4",giving a scrapless design (1/2" wide I-section 94) and highcross-sectional area with 3/4" center leg 132 and winding length 15 of11/4". With these dimensions, and approximately twelve turns of primarywire, one achieves an inductance Lp1 of approximately 160 uH at afrequency of 30 KHz, requiring a preferred leakage inductance Lpe of 40to 50 uH for the above 75% to 80% condition, and Cp of 6 uF for adischarge frequency of 10 KHz.

FIG. 23b depicts an approximately full scale side view of the resonatinginductor 110, with the approximate dimensions shown and an air-gap 129of approximately 1/4" to provide the required inductance Lpe of 30 to 60uH. Preferably, the inductor is made of low-loss ferrite material. Withthe eleven turns of wire 110a shown and a discharge frequency of 10 KHz,maximum flux density Bm for Vp of 350 volts will be about 0.4 Tesla.Preferably, the total series AC resistance of the resonator winding 110aand the coil primary (101) and secondary windings (2a) be about 20milliohms (mohms), i.e. 10 to 30 mohms, for the 10 KHz spark firing orcoil output shorted condition.

FIGS. 24a and 24b depict top and side views of the core of preferredcompact coils made of ferrite or other shapeable material. For thedimensions shown in FIG. 24a, D is 23/8" making it ideal for the layoutof FIG. 23, which would imply a length L2 of the plate of 43/4" whichwould more optimally accommodate the preferred 21/2" diameter resonatinginductor 110 and the switches S1 through S4. Note that for the coils ofFIG. 23a, dimension L2 would be 5" to accommodate pairs of them asshown.

In the preferred embodiment of FIG. 24a center post 132a is 7/8" forferrite material, assuming primary wire of approximately eleven turns,Np=11, and secondary turns Ns=600. A round post as shown allows for thesomewhat smaller window 133a shown. These dimensions can be reduced if amaterial of higher saturation flux density is used, but it must have aneffective permeability of a minimum of approximately 250 at 30 KHz tohave a minimum inductance Lp1 of 150 uH at 30 KHz for Np approximatelyequal to ten turns. Currently available powdered iron is limited to apermeability of 90.

With reference to FIG. 24b the window length 15 is arbitrary since weare not dealing with a lamination (of scrapless design), but a powderedtype material. In this case, assuming Ns=600, one could preferablyselect 15=11/2", which would allow one to wind the secondary turns 2a(see FIG. 23a) with eight layers of preferably 29 gauge copper wire forminimum AC resistance, versus 10 layers of 30 gauge wire for the windowdimensions of FIG. 23a.

FIG. 25 is an approximately full scale drawing of an end view of acompact coil in its completed, encapsulated form with a preferred highvoltage tower 48. The primary winding, preferably of strip copper,comprises one layer with ends 112a, 112b emerging out of the bottom andtop as shown. With reference to FIG. 23, end 112a connects to switch pad126 of S1 (assuming coil is in the T1 position), and end 112b to pad124.

Preferably the overall width E is approximately equal to or less than 2"(17/8" shown), which is achieved in part by placing the tower 48 suchthat its center terminal 29a is vertically above (and preferablyslightly inwards) of the last winding layer of the secondary winding 2a.The encapsulant 138 may cover the top of the core 134 but should notcover the bottom 139 which is preferably heat sunk to the plate 120(FIGS. 23, 26).

In the fragmentary view of FIG. 25a is shown a different placement ofthe high voltage tower 48 to a corner adjacent to an end section 134a ofthe core to make for a somewhat more compact design of minimum "E"dimension.

FIG. 26 is an approximately full scale side view of the coil assembly ofFIG. 23 showing a preferred embodiment of mounting and holding of thevarious parts. In this embodiment, the coils T1, T2, T3, T4 aresandwiched between two plates, plate 120, the bottom mounting and heatsink plate, and plate 130, the top plate which acts also as a electricalground for the shields 53 of the preferred shielded spark plug wire 52.Plate 130 can also act as a secondary heat sink by being bolted to plate120 with heavy metallic bolts required for sandwiching the two plates.Plates 120 and 130 preferably have containing lips 120a and 130a to holdthe coils and resonating inductor 110 in place.

With respect to the grounding plate 130, the high voltage tower openings136, in combination with the towers 48, can easily be constructed suchas to accommodate the shielded type spark plug boots in common use inGerman vehicles, i.e., the coil end of the spark plug wire having ametallic boot similar to the one on the spark plug end, except that theboot would make its electrical contact on its outside with the insideedge of the opening 136.

It should be noted with respect to FIGS. 23 and 26 that the orientationof the coils T1 through T4 are such as to require an integer number ofturns Np of the primary winding 101. This is especially important inminimizing losses for the case that the core material comprised ofcenter post 132, sidewall 134, and end cap 94 is of electricallyconductive material, such as laminated SiFe material.

It should be further noted that the coil invention disclosed herein hasmany features, details, and applications, the essentials of which can bemore succinctly disclosed in terms of the single coil of FIG. 4, forexample, described in a more generic way along with the coil assembly ofFIG. 21, wherein the primary winding of the single coil, and theresonating inductor of the coil assembly, are designated as theprincipal leakage inductance comprising leakage inductor of inductanceLpe, and the means of coupling to the one or more secondary windings iseither directly through magnetic flux coupling between said principalleakage inductance winding 1 and the secondary high voltage winding 2(of FIG. 4 for example), or indirectly by means of one or moreextensions of said leakage winding, i.e. extension sections primarywindings 101 extending from the principal leakage winding 110 (of FIGS.17a and 23, for example), said sections comprising one or more primarywindings 101 coupled to one or more secondary windings 2a of FIG. 17a or102 of FIG. 23, for example.

FInally, it is particularly emphasized with regard to the presentinvention, that since certain changes may be made in the above apparatusand method without departing from the scope of the invention hereininvolved, it is intended that all matter contained in the abovedescription, or shown in the accompanying drawings, shall be interpretedin an illustrative and not in a limiting sense.

What is claimed is:
 1. An ignition coil system for a capacitivedischarge ignition system including at least one discharge capacitormeans, at least one switch means, and at least one ignition coilincluding a primary high current winding means with a principal leakageinductor of inductance value L_(pe) coupled to at least one secondaryhigh voltage winding by one of a) direct coupling through magnetic flux,or b) indirect coupling through primary winding extensions of saidprincipal leakage winding with said extensions comprising a primarywinding portion closely coupled to at least one secondary winding.saidignition coil system constructed and arranged to perform two functions,a) a high voltage breakdown discharge function whereby a high voltage ofabout 15 kV to 45 kV is produced between high voltage terminals of saidat least one secondary winding means to break down a dielectric across aspark gap, and b) an energy delivery function whereby high spark currentof order of magnitude of one amp flows across said spark gap. andwherein, consistent with the above, said ignition coil system is furtherconstructed and arranged such that the structures controlling each ofthe open circuit high voltage breakdown discharge function and the highcurrent spark discharge function are specified separately according to1), 2), and/or 3) below, where: 1) for low saturation ferrite typematerial, the magnetic core section on which the secondary winding iswound is constructed and arranged such that for the peak of said highvoltage the maximum magnetic flux density B_(s) (at 60 degrees F.) insaid core is within 30% of the level given by B_(smax), where:

    B.sub.smax =[K/UF][V.sub.p /(2f.sub.oc N.sub.p A.sub.s)]

where k is the coupling coefficient, V_(p) is the voltage to which thedischarge capacitor is charged, f_(oc) is the open circuit high voltagefrequency, N_(p) is the number of primary winding turns, A_(s) is thearea of the core on which the secondary winding is wound, and UF is theunity factor given by UF=[1+N² C_(s) /C_(p) ], and 2) for low saturationferrite type material, the magnetic core section on which the principalleakage inductance winding is wound is constructed and arranged suchthat for the peak of said high spark discharge current the maximummagnetic flux density B_(p) (at 60 degrees F) in said core is within 30%of the level given by B_(pmax), where

    B.sub.pmax =V.sub.p /[2(pi)f.sub.cc N.sub.p A.sub.p ]

where f_(cc) is the short circuit high current spark discharge frequencyand A_(p) is the area of the core on which said principal leakageinductance is wound, pi=3.142, and 3) for core material of highsaturation flux density, i.e. non-ferrite type, the magnetic coresection on which the secondary winding is wound is constructed andarranged such that at the open circuit frequency f_(oc) the open circuitprimary inductance L_(pl) which is directly coupled to said secondarywinding is equal to or greater than three times the leakage inductanceL_(pe), whereby the circuit parameters and magnetic material propertiesand dimensions are enabled to be further selected to produce moreoptimized operation of said ignition coil system with low electricallosses and minimum sizing of magnetic parts, said magnetic partscomprising materials selected from the class of a) ferrite typematerials satisfying one or both of the above relationships 1) and 2),and b) non-ferrite materials of higher magnetic saturation flux densitysatisfying the above relationship 3).
 2. A system as defined in claim 1wherein the ignition coil system comprises at least one ignition coilwith a principal leakage inductor directly coupled to a secondary highvoltage winding, and wherein said principal leakage inductor comprises aprimary winding wound about a separate primary winding core of windingcross-sectional area A_(p) and said secondary winding is wound about aseparate secondary winding core of area A_(s),said separate primary andsecondary cores constructed and arranged such that at least some of theprimary core magnetic flux produced when the primary winding is excitedby means of an external voltage V_(p) producing primary winding currentI_(p), is directly coupled to the secondary winding core to excite thesecondary winding to induce voltage therein, the ratio of the areas ofthe primary core A_(p) to the secondary core area A_(s) being between1.5 and 3.0.
 3. A system as defined in claim 2 wherein said primarywinding has turns N_(p) of between 5 and 15, and the primary winding hasa number of turns N_(s) such that the secondary to primary turns ratioN, equal to N_(s) /N_(p), is between 25 and 75, both N_(p) and N beingmore precisely selected depending on the required value of the peaksecondary voltage V_(s) and the value of the primary winding peakvoltage V_(p), also equal to the voltage to which the capacitor means ofthe capacitive discharge system is charged.
 4. A system as defined inclaim 1 wherein the ignition coil system comprises a primary windingportion principal leakage inductor of turns N_(p) and of inductanceL_(pe) coupled indirectly through primary winding extensions, each ofturns N_(p1) wound on one compact core per extension with secondary highvoltage windings of turns N_(s) and turns ratio N wound on eachextension and directly coupled to said primary winding extensions, saidcompact coils whose leakage inductance L_(pel) is about equal to or lessthan one tenth of L_(pe), and wherein switch means comprises one switchS_(i) per compact coil Ti connecting one end of the primary windingextension to ground either directly or indirectly through a pathincluding capacitor means and/or principal leakage inductor, said systemas defined above comprising a distributorless ignition system in thatwhen switch Si is turned on, compact coil T_(i) is energized throughcapacitor means charged to voltage V_(p) to produce a high breakdownvoltage Va and one or more sparks at the secondary winding terminals byprimary current being conducted through said compact coil's primarywinding and the principal leakage inductor without the remaining compactcoils being energized to create breakdown sparks.
 5. A system as definedin either of claims 3 or 4 wherein V_(p) is between 300 and 400 volts,V_(s) is approximately 30 kV, Np and Np1 are each between 7 and 13, andN is between 45 and
 75. 6. A system as defined in claim 5 whereincapacitor means of capacitance C_(p) is selected in combination with a)a total capacitance C_(s) of said secondary windings and othercapacitances connected to secondary winding terminals, and b) turnsratio N, such that the conditions of voltage doubling are satisfied byconstruction of the system such that the ratio [P_(N) 2)*Cs/Cp] be lessthan 0.2.
 7. A system as defined in claim 6 wherein leakage inductanceLpe is between 30 and 60 uH, C_(p) is approximately equal to 6 uF, C_(s)is between 100 and 300 pF, and the ignition circuit discharge frequencyfcc is approximately 10 kHz.
 8. A system as defined in claim 7 whereinsaid capacitive discharge circuit is multi pulsing capacitive dischargecircuit further including a recharge circuit including a capacitor ofcapacitance C_(e), and inductor of inductance L_(e), and a diode, toprovide closely spaced, i.e. 200 to 500 microsecond (usec) intervalspark pulses of approximately constant or slowly increasing intervalbetween pulses.
 9. A system as defined in claim 8 wherein capacitivedischarge circuit is of the or ACD topology in which switch means,comprising a SCR and a parallel diode, are connected between oneterminal of one or more primary windings directly coupled to one or moresecondary windings and ground, and the other one or more primary windingterminals are each connected in series with the leakage inductor L_(pe)and capacitor C_(p) through a common node.
 10. A system as defined inclaim 9 wherein leakage inductor L_(pe) is connected between ground andcapacitor C_(p), and to a node between L_(pe) and Cp is connected a fastturn-off circuit comprising a high voltage diode, a one to five kilo ohm(kohm) one to two watt resistor, a capacitor of value of 0.05 to 0.2 uF,and a gate resistor of value 100 to 500 ohm, and one end of the gateresistor is connected to SCR gates either directly for one SCR and onecoil or through isolating diodes for more than one SCR gates of morethan one compact coil T_(i).
 11. A system as defined in claim 10including a snubber means comprising an in series capacitor and resistorconnected preferably between feed voltage terminal where rechargecircuit connects to ACD circuit or said common node and ground.
 12. Asystem as defined in claim 11 wherein Le is between 5 and 30 millihenry(mH), C_(e) is between 0.2 and 0.6 of C_(p), and the snubber capacitorof said snubber means is of the order of magnitude of 0.05 uF.
 13. Asystem as defined in claim 3 wherein its coil's separate primary andsecondary cores are two different core halves which define a closedmagnetic path within the core material when they are used as a pair, thecores and other selected from the class of pot cores, E cores, ETDcores, PM cores and other related closed cores having an inner windingcenter post, an end section, and a sidewall, the primary winding woundon the center post of area A_(p) of the primary core and the secondarywinding wound on the center post of the secondary core of area A_(s),and wherein the two core halves are butted against each other linkingmagnetic flux via their center posts and sidewalls, with the outerdiameter of the two sidewalls being essentially equal to provide for awider winding window of width Ws for the secondary winding and anarrower primary winding window W_(p).
 14. A system as defined in claim13 wherein the primary winding is made up of two layers of primary wire.15. A system as defined in claim 14 wherein the primary wire is madefrom the class of wire whose AC resistance at the closed circuit sparkdischarge frequency fcc is less than a factor of two of its DC (directcurrent) resistance, said class including Litz wire, and rectangularstrip conductor whose thickness is between approximately 1 and 11/2times the skin depth of the strip material at the operating frequencyfcc, and wherein the diameter of the secondary wire is equal to aboutone third the skin depth.
 16. A system as defined in claim 15 whereinW_(p) is approximately 1/4 inch and Ws is approximately 1/2 inch.
 17. Asystem as defined in claim 16 wherein the secondary winding is layeredalong the length of its center post and has a variable turns N_(ti) perith layer and wherein over some range of values of layers the turns perlayer N_(ti) decreases so as to increase the clearance of the highervoltage turns from the (grounded) core end walls and sidewalls.
 18. Asystem as defined in claim 13 wherein the coil winding secondary windingcapacitance C_(sc) is utilized for improving the coil capacitive sparkignition capability by constructing the high voltage lead connecting thecoil output terminal to the spark gap to lower the frequency oftransmission of the capacitive spark to 5 to 30 MHz so that is deliveredwith small attenuation to the spark gap while electrical energy flowingabove 30 MHz is strongly attenuated.
 19. A system as defined in claim 13wherein said high voltage lead is contained in a grounded shieldterminating at a coil core outer surface or at a metal plate containingor attached to the core and at an outer conducting shell of a spark plugmeans containing said spark gap so as to produce very low EMI.
 20. Asystem as defined in claim 1 wherein the secondary winding open circuithigh voltage output is of positive polarity, versus the conventionalnegative polarity, in order to minimize plug fouling, especially ofplugs with a toroidal spark gap.
 21. A system as defined in either ofclaims 3 or 4 which uses a spark plug for the device containing thespark gap which is a toroidal gap electric field focussing lens typespark plug with a firing end button tip of small diameter of between0.20" and 0.35" and made of erosion resistant material of the class ofNickel alloy, Tungsten-Nickel-Iron, Tungsten-Nickel-Copper, and othersimilar erosion resistant materials, and with the plug ground ring madeup of similar material, to be able to withstand the higher spark powerand higher total energy per spark firing made possible by the presentignition system.
 22. The plug as defined in claim 21 wherein its plugcapacitance C_(sp) is about 40 pf and the firing end of the plug has anapproximately 0.1" spark gap which is at an approximately 45 degreeangle to the vertical axis defined by the plug length to minimize thechances of plug fouling.
 23. A system as defined in claim 21 incombination with an engine wherein many spark pulses per ignition sparkfiring are used, 10 to 20 pulses at low RPM of about 600 RPM of theengine, dropping to two to five closely spaced pulses of approximately250 microseconds (usec) interval at 6,000 RPM.
 24. A system as definedin claim 23 wherein sufficient such spark pulses are provided per firingto ignite at least half of the toroidal volume of the said focussinglens type plug at low RPM engine operation.
 25. A system as defined inclaim 24 wherein there is provided a variable spark pulse timing withgradually increasing time between pulses with subsequent pulsesincreasing by a factor of about two over the entire spark firing period.26. A system as defined in claim 25 wherein an initial time betweenpulses of approximately 200 usec is used which increase to approximately400 usec at the end of the tenth pulse and to approximately 500 usec atthe end of the 15th pulse.
 27. A system as defined in claim 4 andfurther comprising an ACD circuit with one or more compact coils whosenon-switched primary winding end terminals are all connected to a commonnode point P of voltage V_(p) to which one end of capacitor means Cp isconnected and whose other end is connected to the principal orresonating inductor of inductance L_(pe) whose other end is gounded, andan isolating choke of inductance Le is connected between node P and apower supply means working to maintain voltage V_(p).
 28. A system asdefined in claim 27 wherein inductance Le has an in series diodeconnected to one of its terminals and a capacitor of capacitance Ceconnected between it and said power supply means and ground, defining arecharge circuit, such that when the circuit is energized by firing(closing) a switch means Si of compact coil Ti, energy on capacitor Cebegins to discharge through inductor Le with current Ire to rechargecapacitor Cp, with current Ire reaching near or zero current prior tosubsequent firing of Si.
 29. A system as defined in claim 28 whereinsaid compact coils are comprised of a concentric winding of single layerof primary winding of turns N_(pl) about a center core post and Ntlayers of secondary winding of turns Ns wound over the primary winding.30. A system as defined in claim 29 wherein diameter D and height L ofcore of compact coils are each approximately 21/2 inches and center postarea A_(ps) is approximately 1/2 square inch, i.e. between 3/8 and 5/8square inch.
 31. A system as defined in claim 30 wherein core is ascrapless E-I laminated core with winding window dimensions W and 15equal to 1/2 inch (for width W) and 11/4 inch for length
 15. 32. Asystem as defined in claim 31 wherein laminations are of SiFe ofthickness of approximately seven mils.
 33. A system as defined in claim30 wherein N_(p) and N_(pl) are each approximately 10 turns, N isapproximately 55, and the number of secondary layers Nt is between 7 and13.
 34. A system as defined in claim 33 wherein primary winding wire isof rectangular cross-section of approximately 0.10" by 0.036" andsecondary winding wire is approximately 30 gauge wire.
 35. A system asdefined in claim 30 wherein core material of resonating inductor isferrite of approximate diameter D of 21/2 inches and approximate heightof 11/2 inch.
 36. A system as defined in claim 27 wherein four compactcoils T1, T2, T3, T4 are used and mounted on a rectangular base platewith their respective spark plug towers located on the outside part ofthe plate, and wherein a section is defined between pairs T1/T2 andT3/T4 of the coils in which is mounted the capacitor Cp, and theresonating inductor L_(pe) and the four switches S1, S2, S3, S4 whichare mounted on the base plate which acts also as a heat sink to coolinductor L_(pe), the switches, as well as the coils.
 37. A system asdefined in claim 36 wherein a top plate is used for sandwiching saidcoils and other parts between itself and said base plate, the top platealso able to function as a ground plate for grounding any shields ofhigh voltage shielded wire that may be used and also able to function asan additional heat sink for the parts sandwiched between it and the baseplate.
 38. A system as defined in claim 36 wherein switches S1 throughS4 are each SCRs with parallel diodes, and wherein primary winding endwire sections are connected to a respective switch via a conductive padand to one end of a pad at common node point P such that the primaryturns defines an integer number of primary turns.
 39. A system asdefined in claim 30 wherein said compact coils are encapsulated with lowdielectric constant encapsulant, i.e. dielectric constant of about 3,said encapsulant forming a high voltage tower whose center isessentially vertically above the outer last winding layer of thesecondary winding such that the overall end width E is approximatelyequal to and less than 2.0".
 40. A system as defined in claim 36 whereincompact coils are encapsulated and have overall cross-sectionaldimensions of approximately 21/2" by 2" to define the overall coilassembly cross-sectional dimension of approximately 5" by 6".
 41. Asystem as defined in claim 28 wherein said compact coils are constructedand arranged so as to each be mounted on top of a spark plug.
 42. Asystem as defined in claim 41 wherein primary and secondary windings arewound side-by-side over a center core post.
 43. A system as defined inclaim 42 wherein primary winding turns are approximately 8 in number andare wound on the side away from the spark plug location so that theprimary winding turns emerge from the back of the compact coil for easyconnection to the respective switch and to the node point P.
 44. Asystem as defined in claim 35 wherein mean center post diameter ofcompact coils and resonating inductor are approximately 0.75" and 1.5"respectively.
 45. A system as defined in claim 44 wherein widths of sidewall and slot in which wire is wound are each approximately 1/4" wide,the length along which wire is wound is approximately 7/8", and the airgap, which sets inductance L_(pe) for the approximately ten turns ofwire required on the basis of magnetic saturation, is about 1/4", andthe wire is wound in two layers.
 46. A system as defined in claim 13wherein said primary core is made of ferrite, ferrite-like, NiFe, orother low loss material and said secondary core is made of a materialselected from of the class of SiFe, powdered iron, and other similarlylow cost material.
 47. A system as defined in claim 13 wherein aseparate outer casing for the core material is used and selected fromthe class consisting of plastic with ferrite loading, NiFe, SiFe,powdered iron, metallic glass, any of the above in either cast or tapeform.
 48. The system defined in claim 15 in combination with an MPCDignition circuit including recharge circuit means for providing 250 to500 usec spark pulses of approximately constant or slowly decayingamplitude, and constructed and arranged such that if the first sparkpulse misfires the coil will permit the recharge circuit to raise itsprimary, and hence secondary voltage of the second pulse to a highervalue.